The hydraulic oscillator is used to solve the problems of slow drilling and stuck drilling caused by excessive friction undergound. In the case of the screw motor selected, the performance of the oscillator are mainly determined by the size of moving and fixed valve holes and the eccentricity distance of the moving valve hole. If the parameter is not appropriate, for example, the oscillation force is too small to solve the problem caused by excessive friction. It will affect the drilling speed and delay the completion time of drilling. If the oscillation force is so large,it will affect the normal work of other downhole tools，or even cause serious safety accidents. Fluent grid and UDF were used to simulate the motion state of the valve under actual working condition, and calculate the pressure drop. The correctness was verified by experimental data. In order to obtain the pressure drop under different parameters of structure performance, the size of moving and fixed valve holes and the eccentricity distance of the moving valve hole were disigned by orthogonal test.According to the requirement,the combination of structural parameters can be selected with the mean pressure drop between 2~45 MPa. The research results have important guiding significance for the design of hydraulic oscillators.