When technological discontinuities disrupt markets, firms have incentives to form alliances in order to gain access to relevant new resources. Such alliances for new resources add to a firm′s alliance portfolio, which is a set of partnerships that the firm manages collectively. An alliance portfolio aggregates all needed network recourses, transferable as capital, information and technology, and other social-specific resources, such as legitimacy, status and reputation. It is well recognized that an alliance portfolio itself has become the source of sustainable competitive advantage over competitors. However, with the change of the external environment and the increase of the diversity of partners, the problem of "capability trap" is faced on the basis of the accumulation of alliance core competence. Therefore, in order to overcome the capability rigidity and the ability trap of leapfrogging, reconfiguring alliance portfolio efficiently has become an urgent and challenging issue for all firms.
     However, some scholars offer two contrasting perspectives on the reconfiguration of alliance portfolio. On the one hand, alliance portfolio reconfiguration leads to disruption, and thus it increases the risk of subsequent innovation project termination. Alliance partners tend over time to develop interfirm routines for working together. In an alliance that is reconfigured after formation these routines are likely to be upset—disrupting established patterns of interaction and coordination mechanisms that all crucial to alliance effectiveness. On the other hand, portfolio reconfiguration leads to adaptation; therefore, it decreases this risk. Alliances derive their value from allowing collaborating partners to gain access to new knowledge and technologies, to share risk, or to pool resources and capabilities. Changes in the environment in which an alliance operates may erode the value of the initial configuration of partners established at the time of alliance formation. Alliance portfolio reconfiguration, whether by adding a new member, or by dropping one, may thus be an opportunity to recalibrate the alliance to a changing environment. In contingency-theory this is seen as a "structural adjustment to regain fit", which may actually be beneficial.
     Based on network theory and dynamic capability theory, in view of the inadequacy of existing research, this study analyzes the effect of alliance portfolio reconfiguration on cooperative innovation performance. Furthermore, a theoretical model, comprised of the direct effect of alliance portfolio reconfiguration on cooperative innovation performance, is proposed to examine the mediating effect of alliance legitimacy and the moderated mediator role of environmental dynamism on the relationship between alliance portfolio reconfiguration on cooperative innovation performance. The theoretical model reveals the mechanisms that alliance portfolio reconfiguration affects cooperative innovation performance.
    What is more, the questionnaires, developed by scales in literature from authoritative journals and field investigations, are filled in by the middle, and senior managers from 650 firms in strategic emerging industries of China, and 336 of which are valid. And then, related data analysis methods, such as reliability test, validity test, hierarchical regression analyses, are adopted to validate the proposed hypotheses and theoretical model via STATA 14.0 and Mplus 7.0.
    The empirical evidences show that: (1) Alliance portfolio functional reconfiguration can significantly (p＜0.01) enhance cooperative innovation performance, and alliance portfolio structural reconfiguration can also significantly (p＜0.01) enhance cooperative innovation performance; (2) The remarkably positive relationship between alliance portfolio reconfiguration (alliance portfolio functional reconfiguration and alliance portfolio structural reconfiguration) and alliance legitimacy is observed (p＜0.01), and the similar result exists between alliance legitimacy and cooperative innovation performance (p＜0.01). Also, the significance of the positive relationship between alliance portfolio reconfiguration (alliance portfolio functional reconfiguration and alliance portfolio structural reconfiguration) and cooperative innovation performance is weakened (p＜0.05) because alliance legitimacy is involved in the regression model. That is to say, alliance legitimacy plays a partly mediating role in the relationship between alliance portfolio reconfiguration (alliance portfolio functional reconfiguration and alliance portfolio structural reconfiguration) and cooperative innovation performance; (3) Environmental dynamism positively moderates the relationship between alliance portfolio functional reconfiguration and cooperative innovation performance, and the same effect is verified on the relationship between alliance portfolio structural reconfiguration and cooperative innovation performance. Additionally, environmental dynamism moderates the mediating effect of alliance legitimacy on alliance portfolio functional reconfiguration on cooperative innovation performance, and environmental dynamism moderates the mediating effect of alliance legitimacy on alliance portfolio structural reconfiguration on cooperative innovation performance.
   Overall, the research conclusions of this article deepen the understanding of the basic question of how alliance portfolio reconfiguration affect cooperative innovation performance. The contributions are as follow: (1) We select alliance portfolio as research objects, that is to say, treat all the alliance partners of a firm as a whole, and regard alliance portfolio reconfiguration as the antecedent variable of innovation performance. That transcends the limit that most existing literature focuses on the management of the single alliance, and expands the theoretical research on alliance management from a broader perspective. (2) This study found that both the functional reconfiguration and structural reconfiguration of alliance portfolio have significantly positive impacts cooperative innovation performance．The finding deepens our understanding of the dynamic management process of alliance portfolio and expands the application of the resource based theory in alliance portfolio research． Therefore, it provides certain reference for further research on dynamic management of alliance portfolio. (3) This study also verifies the mediating role of alliance legitimacy on the relationship between alliance portfolio reconfiguration and cooperative innovation performance through integrating network theory and institution theory. It further reveals the internal impact mechanism of alliance portfolio reconfiguration and cooperative innovation performance as well as deepens our understanding to the impact mechanism of legitimacy perception. (4) Based on the alliance network mechanisms, this research explores the influence process of alliance portfolio reconfiguration and cooperative innovation performance, and discusses the moderation effect of environmental dynamism in this process. In addition, environmental dynamism moderates the mediating effect of alliance legitimacy on alliance portfolio reconfiguration and cooperative innovation performance. By doing this, it extends the scope of contingency theory, and helps the research area of alliance portfolio moving forward, thus provides us a more comprehensive and in-depth understanding about alliance strategy and behavior.