Abstract: Based on the study of the needle bar mechani sm in computerized embroidery machine, the mass cen ter position equation of the needle bar mechanism is deduced.The mass center cur ve of the n eedle bar mechanism is studied.The velocity,acceleration and the inertial force are calculated.On the basis of the displacement analysis of the needle bar mech anism, the theoretical basis is given out for the improvement design of the need le bar mechanism.