Abstract: The paper took the loose joint between crank and linkage of membrane pump as a wear fault and built dynamic model of cross slide of membrane pump according to contact force model in contact-separation states.On the basis it used Runge-Kutta method to make numerical simulation and gave dynamic response of displacement-speed of cross slide under different parameters,namely different crank rotate speeds,different wear rates and different liquid pressures.The result of the study indicated that the dynamic response of loose joint between crank and linkage of membrane pump is mainly influenced by crank rotate speeds,and it is also related with wear rate and liquid pressure of piston surface.