In order to study the step response time of the 2D servo valve which the form of high and low pressure hole of the valve core is the circular groove hole, the pendulum wheel step response unit was designed,and the experimental research of the response characteristics and stability analysis was completed of the the spool displacement of the 2D servo valve with the circular groove. The experimental results show that the pendulum wheel step response unit can give an ideal step signal,when the input pressure is 21 MPa, the step signal is 09 ms,the step response time of 2D servo valve of the circular groove is 2 ms.