We study explicit incentive and implicit incentive on the risk taking of the open end mutual fund whose compensation contract is Performance based Fee. By a game model with mixedstrategy, we argue that the probability of holding risk asset of the fund with better midyear performance is higher than that of the fund with bad midyear performance. We analyze the effect of the return gap between risk asset and benchmark portfolio，performance gap, volatility of the risk asset and the degree of explicit and implicit incentive in the risk taking behavior.