This paper investigates the volume-synchronized probability of informed trading ( VPIN) for the stocks listed in CSI 300 index. Using VPIN as a proxy of information asymmetry,we examine the risk premia of information asymmetry and the relation between information asymmetry and information uncertainty. Our empirical results show that: ( 1) An increases in VPIN results in a larger bid-ask spread and liquidity risk,leading to a pounced risk premia in both cross-sectional and time series analyses. ( 2) VPIN dominates the factor of information uncertainty in explaining the excessive return,while information uncertainty also generates co-directional effects on VPIN. ( 3) VPIN remains significant after we control information uncertainty,size,momentum factors. Meanwhile,Fama-Macbeth analysis shows that the VPIN has no endogenous problem with traditional risk factors and is orthogonal to them. ( 4) Unusual risk premia and trading volumes which occur before companies’major announcements can be captured by the synchronized abnormal VPIN.