Abstract: Faced with fierce market competition, the acquisition of tacit knowledge from virtual innovation community is crucial to the improvement of corporate market competitiveness. Virtual community rewards as an important measure for communities to promote tacit knowledge sharing. Although the issue of the impact of community rewards on knowledge sharing has won widespread attention and research, there are still some limitations. On the one hand, there are three controversial views on the impact of community rewards on knowledge sharing, such as negative impact, positive impact and no significant impact. On the other hand, intrinsic motivations play an important role in the process of sharing tacit knowledge. However, few scholars have studied the transformation between virtual community rewards and intrinsic motivation or the internal mechanism of intrinsic motivation between virtual community reward and tacit knowledge sharing.Virtual community reward refers to formal rewards such as community points/ ranking, badges, gifts, cash, etc., provided by administrators of virtual communities for users’ knowledge sharing behaviors, with signal function and external incentives function. Under the low-level virtual community reward, the virtual community reward as a compensatory benefit is far lower than the cost of sharing tacit knowledge. It can promote user to share tacit knowledge by conveying community’s support and encouragement to users through its signal function. With the increase of rewards, the external incentive function dominates gradually and its destructive impact on user’s intrinsic motivation is strengthened. When the constructive effect of community signal equals to the destructive effect of external incentive, users’ motivations to share tacit knowledge reach the maximum. With the continuing increase of rewards, the destructive effect of external incentive exceeds the constructive effect of community signal and rewards begin to have a negative effect on users’ tacit knowledge sharing. Therefore, we propose H1: There is an inverse U-shape relationship between virtual community rewards and tacit knowledge sharing.Sharing tacit knowledge among users is quite challenging and can bring users more enjoyment and self-efficacy. So, we assume intrinsic motivation, including enjoyment and self-efficacy exist mediation between virtual community rewards and tacit knowledge sharing. Scholars point out intrinsic motivation is a dynamic process which changes dynamically with the change of external stimulus. The different functions of different levels of virtual community reward can have different effects on user’s intrinsic motivation, which may lead to different tacit knowledge sharing levels. The signal function of low-level virtual community reward can make user perceive more enjoyment and self-efficacy during the process of sharing tacit knowledge and thus promote them sharing more tacit knowledge. Conversely, the external incentive function of high-level virtual community reward can reduce user’s sense of enjoyment and self-efficacy of sharing tacit knowledge. Moreover, the temporary compliance of virtual community reward determines that it can only stimulate tacit knowledge sharing in the short term and has no long-term effect on tacit knowledge sharing. With the increase of virtual community reward, its external incentive function becomes more and more prominent. And users are more inclined to regard their tacit knowledge sharing as a transaction which decreases their senses of enjoyment and self-efficacy, leading to serious erosion of users’ intrinsic motivations of sharing tacit knowledge. When the destructive effect of external incentive function is higher than the constructive effect of signal function, the positive influence of virtual community rewards on users’ tacit knowledge sharing is reduced. Therefore, we propose H2; Enjoyment mediates the relationship between virtual community reward and users’ tacit knowledge sharing and H3:Self-efficacy mediates the relationship between virtual community reward and users’ tacit knowledge sharing.The paper uses empirical study to test hypotheses. The paper takes 429 data as sample collected from four virtual innovation communities, such as MIUI community, OPPO community, VIVO community and Glory of Kings community. Multiple regression model is used to test the nonlinear relationship between virtual community reward and tacit knowledge sharing. And, multiple regression model and Bootstrap method are simultaneously used to test the mediation of intrinsic motivation between virtual community rewards and tacit knowledge sharing. Results show that there is an inverted U-shaped curve relationship between virtual community rewards and tacit knowledge sharing; enjoyment and self-efficacy play complete mediation between virtual community rewards and tacit knowledge sharing.There are mainly two theoretical contributions. On the one hand, this paper proposes and confirms that there is an inverse U-shape relationship between virtual community rewards and tacit knowledge sharing, which is distinct from the linear relationship results that most existing studies declare. Besides, this conclusion will encourage the debate about effects of virtual community rewards on tacit knowledge sharing and prompt the development of the theory. On the other hand, this paper demonstrates that intrinsic motivations fully mediate the relationship between virtual community rewards and tacit knowledge sharing. In the past, few scholars explore the influence mechanism of virtual community rewards on tacit knowledge sharing. We confirm that virtual community rewards impact tacit knowledge sharing according to mediating effects of intrinsic motivations, which broadens and contributes to existing related literature.Based upon the results, we have suggestions for firms to promote tacit knowledge sharing in virtual communities. First of all, the level of virtual community reward is not the higher the better and too high rewards are to weaken users’ intrinsic motivations to share tacit knowledge. For the purpose of determining the appropriate level of rewards, we can use Bayesian method to carry out comparison analysis for panel data including rewards level and tacit knowledge sharing. Moreover, Virtual communities can take some measures to enhance knowledge disseminators’ self-efficacy and enjoyment during tacit knowledge sharing in order to increase their intentions to share tacit knowledge. For example, virtual communities can design additional different forms of contests including knowledge and innovative contests besides community basic activities to enhance users’ self-efficacy and enjoyment and then inspire their intrinsic motivations to share tacit knowledge sharing.

Key words: virtual community rewards, tacit knowledge, intrinsic motivation, inverted U-shaped