Abstract: By setting up the dynamic principalagent model， influencing factors of the incentive mechanism were researched on the basis of performance， and the incentive efficiency of openend fund family was optimized. The results shown that the efficiency loss resulted from incentive mechanism will increase as the degree of information transparency in security market reduces， while decrease with the increase of the investment horizon. And the reputation mechanism set up by the fund family will exert a kind of favorable reputation transfer function， which will promote the incentive efficiency to increase， and achieve Pareto optimality under the given conditions.The practical applications of the model are revealed at last

Key words: fund family, reputation mechanism, openend fund, incentive efficiency, principalagent model