For Stewart parallel mechanism, cosimulation was analyzed theoretically based on ADAMS and MATLAB/Simulink. Through comparing it with other design schemes, the advantages of the cosimulation were obtained. Cosimulation was done by aimed at 6UCU Stewart, for Simulink control model of symmetrical valve controlling asymmetric cylinder by using respectively ADAMS kinematics model and ADAMS dynamics model. It was obtained that in the joint space control, the model based on ADAMS dynamics has a better simulation result than that based on ADAMS kinematics.