Abstract: To the hydraulic transformer controlled hydraulic motor system, the system transfer function was built based on the system principle, dynamic equation and the linear theory. Theoretical analyzing indicates that the hydraulic transformer controlled hydraulic motor system has minimum phase system characteristic and non-minimum phase system characteristic simultaneously. For the hydraulic transformer with equivalent port, when the hydraulic transformer control angle is less than 30°, the system is the minimum phase system, and when the hydraulic transformer control angle is more than 30°, the system is the non-minimum phase system. Based the hydraulic transformer controlled hydraulic motor system dynamic equations,the simulation result proved that when the hydraulic transformer control angle is more than 30°, the step response of system shows negative response and the characteristics of the non-minimum phase system. The experiment studies validate the results of the theoretical analysis and simulate analysis further. The research indicates that the hydraulic transformer controlled hydraulic motor system is not suitable for the high precision torque and speed control system.