This paper discussed the problem of supervising the price and risk control of mutual fund. Based on the theory of fuzzy stochastic system, the risk measure of mutual fund price was proposed. The behaviors of investing under the condition of transact cost were studied. Market supervision and risk control of mutual fund was discussed in the paper. Possibility simulation of efficient transaction time, in which price going up and down to the barrier controlled was completed, the simulation results show that the approach is effective．Some further researches on this problem are presented as a conclusion