Abstract: In order to improve the quality of hydro mechanical variable transmission when shift ing,the control model of HMT has been built up based on the theory of HMT control systems where the ECU control with PID control logic and fuzzy control logic have been adopted separate ly.Under the mechanical control,the output speed changes 17 0%;under the ECU control with PID control logic,the change is only 2 0%;while under the ECU control with fuzzy control logic,the change is only 1 5%.So the fluctuation of output speed has been effectively reduced.