The selflocking torque of electromagnetic balancer has the functions of driving and selflocking,and its evaluation indexes are the work done within a step angle of selflocking torque and the peak value of selflocking torque.On the premise of keeping the parameters of the gear disk unchanged,by establishing a threedimensional model of the selflocking magnetic circuit of the balancing head, based on the transient solver of Ansoft Maxwell-3D,the variation law of the peak value of the selflocking torque,the power done and their ratio under different permanent magnet quantity,material,shape and position parameters was studied by using the finite element analysis method.The results show that the peak value of selflocking torque and the power done in the whole period increase with the increase of the number,length and diameter of the permanent magnet,but decrease with the increase of the gas gap;the ratio of the peak selflocking torque to the power is approximately constant 0.34 when the axial projection of the magnetic circuit is constant,it is approximately 0.31 when the number of permanent magnets change,it decreases exponentially with the increase of the diameter of permanent magnet.