Taking Chinese Ashare listed companies from 2008 to 2017 as the research objects, this paper uses panel Poisson regression to analyze the role of institutional investors in the risk of individual stock abnormal return from the static, dynamic and heterogeneous perspectives. The results show that on the static level of shareholding, the rise in the proportion of institutional investors’ holdings increases abnormal return risk of individual stocks in the future instead of stabilizing the company’s future stock price, and this risk superposition effect is asymmetric, namely, the impact of rising shareholding ratio on stock price crash risk is more obvious. On the dynamic change of shareholding, “net increase in holdings” of institutions does not boost the current stock price, but “net reduction” aggravates the stock price collapse in the current period. From the perspective of heterogeneity of risk superposition effect, the larger the size of the company (the more convenient the institution is to enter and exit), the stronger the positive impact of institutional ownership on abnormal return risk; and the higher the ownership concentration of institutional investors, the stronger the positive impact. This paper identifies whether institutional investors play the role of “stabilizer” or “booster” in abnormal volatility of capital market, and provides an empirical basis for improving the supervision of institutional investors and preventing abnormal volatility risk of stock price.