The 2D servo valves are famous with its characteristics of excellent dynamic property and high power-to-weight ratio.The valve core rotates and then moves axially under the action of the pilot control oil,therefore,the frictional resistance generated by the 2D gap flow between the valve core and the valve sleeve is an important factor affecting the valves performance.In order to study the influence of 2D gap flow on frictional resistance,theoretical analysis and simulation research were carried out on the right gap flow of a 10-diameter 2D servo valve core.The results show that the frictional resistance on the valve core is closely related to gap width,inlet pressure and velocity of moving wall,the value decreases and then increases with the increase of gap width,which mean an optimal gap width exists and the optimal gap is less than that of one-dimensional gap flow.In addition,the frictional resistance increases with the increase of inlet pressure,however,it increases first and then decreases with the increase of the velocity of the moving wall.The 2D servo valve can achieve a large power-to-weight ratio which is experimentally verified that the startup friction resistance needed to be overcome is only 2.94 N.