Torque converter is a key component of hydro-mechanical transmission system. To improve the workingefficiency of hydro-mechanical transmission system,the lockup and unlock control strategy of torque converter wasdesigned. The dynamic model for lockable torque converter was established,and three types of its working condi-tions,including hydraulic working condition,frictional working condition and mechanical working condition,wereanalyzed,based on the present simulation model for torque converter. The model of lockable torque converter wasapplied to the powertrain system model of a certain tracked engineer vehicle. Under the control strategy of dynamicgear shift,the simulation model was computed from 2 nd gear and upshifted to 6 th gear. The simulation result indi-cates the lockup and unlock control strategy is correct and valid.