Electrohydraulic servo valve can be divided into nozzle flapper servo valve, jet servo valve and direct drive servo valve according to the structure, and the main difference is that different hydraulic amplifiers are selected in the front stage. Cylindrical spool valve pair is generally used as the second stage power amplification stage, and the performance of the spool valve pair also directly affects the performance of the servo valve. Therefore, from the axial and radial combination with zero opening, positive opening, negative opening form, the influence of the spool valve pair fit on the performance of the servo valve was analyzed. At the same time, the influence of the opening of the asymmetric spool valve pair on the performance of the servo valve was analyzed, and the analysis results were verified by experiments.