Under the guidance of the national strategy of innovation-driven development, there have been a number of R D alliances among Chinese companies in recent years. Taking as the research object the companies of the ChiNext market that are both active in R D alliances and innovation activities, we analyzed the mechanism of R D alliances and its impact on innovation. Our results show that R D alliances have a positive effect on technological innovation by using propensity score matching method and difference-in-differences regressions. Companies that have R D alliances are better than companies that have not in the respect of multiple measures that reflect innovation capability. The patent, the invention, technological diversification and innovative breakthroughs metrics show a positive and robust effect of a R D alliance on innovation capability. Moreover, R D alliances have a lagging effect on technological innovation increasing year by year. Furthermore, we also find that the continuity of R D alliance has a learning effect. Compared with one-time R D alliances, continuous R D alliances have a greater role in promoting innovation. In addition, the governance structure of the R D alliance has a moderating effect. Compared with joint-ventures, non-joint ventures have a greater role in promoting innovation. This paper provides theory and empirical evidence for our insight into synergies of R D alliances in Chinese companies. In addition, it also provides meaningful policy implications for China’s government and firms to enhance innovation capability.