Abstract:    The fluctuation of a firm′s R&D (Research and Development) investment has typically caused high adjustment costs, such as researcher hiring and lay-off costs, information spillover risks, overtime costs etc., which will undermine firms′ competitiveness on the long term. Meanwhile, due to severe external innovation financing constraints caused by high information asymmetry and high failure risks, external financing of innovation investment is risky. Internal financing for innovation investment is mainly about firms′ internal cash flow internal, which is highly volatility because it′s sensitive to macro-economic environment, industries cycle and firms′ operating activities change. Thus, firms′ R&D investment face greater financing risk than other capital investment. High financing risk and high adjustment costs arising from inadequate financing force firms to strive to maintain a relatively stable innovation investment during multi-periods. In face of financing uncertainty, R&D investment smoothing is a strategic behavior that using liquid assets with low adjustment costs to support financing support R&D investment with high adjustment costs, which is aim at maintaining sustainability of firms′ innovation investment and avoiding high adjustment costs trigger by R&D investment reduction or suspension. 
   Considering China′s transition economy characteristics, government still has a strong influence and control capability on economic resources and there exists high correlationship between economic policy and firms′ behavior such as financing and investment. In addition, unlike Western developed countries, the introduction and implementation of China′s economic policies is more direct and convenient in terms of political procedures, economic policy uncertainty environment faced by firms located in China. Thus, the research about micro impact of economic policy uncertainty on the firms′ R&D investment smoothing behavior is of great importance for understanding firms′ dynamic characteristics of innovation investment under highly uncertain conditions. 
   Although there are many literatures discussing economic consequences of economic policy uncertainty from macro-perspective and micro perspective, such as unemployment, economic growth, firms′ financing and investment behavior etc., the discussions about the impact of macro-economic policy uncertainty on micro firms′ innovation activities is still limited, especially for the impact of economic policy uncertainty on firms′ R&D investment smoothing from dynamic perspective. The relationship between economic policy uncertainty and firms′ innovation sustainability is still unclear.
   Based on theoretical analysis, the impact of economic policy uncertainty on firms′ R&D investment smoothing mainly through two mechanisms: Firstly, heightening economic policy uncertainty motivate firms′ R&D investment smoothing by increasing R&D project financing risks. Under heightening economic policy uncertainty, both of external financing and internal cash flow would become more unstable and unpredictable. Secondly, heightening economic policy influence on firms′ R&D investment smoothing by changing R&D investment adjustment costs.
   Using the data of Shanghai and Shenzhen A-share listed companies in manufacturing and information technology industries from 2012 to 2016, this paper further empirically studies the impact of China′s economic policy uncertainty on the firms′ R&D investment smoothing by using panel regression model. The results show that the increase of economic policy uncertainty has strengthened the firms′ R&D investment smoothing. Compared with state-owned enterprises and enterprises located in high marketization districts, the strengthening effect is much bigger in private enterprises and enterprises located in low marketization districts. 
   This paper contributes to existing literature in two ways: Firstly, the existing literature mainly focus on the impact of economic policy uncertainty on the single-phase innovation activities from static perspective. This paper expands the research scope of economic policy uncertainty consequences by analyzing the impact of economic policy uncertainty on the several-phases innovation activities characteristics from dynamic perspective. Secondly, the previous research on the influencing factors of R&D investment smoothing behavior mainly focus on firms′ financing constraints and regional financial development level at micro level, the macro influencing factor of R&D investment smoothing is few. This paper enriches the existing literature of R&D investment smoothing by combining the economic policy uncertainty with firms′ R&D investment smoothing behavior, which helps to understand the firms′ R&D investment smoothing behavior adjustment under economic policy uncertainty condition and enrich the research on the correlation between macroeconomic policy and micro firms′ behavior.

Key words: economic policy uncertainty, R&D investment smoothing, interruption risk, adjustment cost