We build a market microstructure model within the framework of Rational Expectations Equilibrium and deliberately factor uncertainty into our model so as to study from the perspective of uncertainty whether and how stock market information asymmetry would contribute to stock crash. Our model demonstrates that market information asymmetry does contribute to stock crash, and that the greater the information asymmetry, the deeper stocks would plunge, the greater the uncertainty in the market, the greater the impact information asymmetry would have on stock crash. We then calculate the probability of informed trading of A equities listed on the Shanghai and Shenzhen stock markets according to the relevant tick data from 2010 to 2015 and use the calculated probability of informed trading as a measure of information asymmetry of the Shanghai and Shenzhen stock markets. And we conduct empirical tests according to the calculated probability of informed trading to find that there exists a significant positive correlation between market information asymmetry and stock crash, and usually the greater the market information asymmetry, the deeper stocks would plunge. In addition, we also formulate uncertainty indexes for A equities listed on the Shanghai and Shenzhen stock markets, using the uncertainty indexes for measuring stock market uncertainty, and in the light of the uncertainty indexes we discover that market uncertainty tends to increase the impact information asymmetry would have on stock crash, i.e. the greater the uncertainty in the market, the greater the impact information asymmetry would have on stock crash. Our findings do not only add to the existing knowledge about the causes of stock crash, but also sheds new light on how to prevent abnormal volatility on stock markets.