In this paper, a new structure of dynamical-filtering roller-type screen pipe based on ordinary gear train is put forward. In light of the working conditions of the oil pump, the operating principle of this kind of screen pipe is presented. Three-dimensional model and computational fluid dynamical (CFD) model for flow filed analysis are established. Then, pressure exerted on the blades of the impeller wheel in the screen pipe is calculated in FLUENT, which yields the torque on the impeller shaft and explains the mechanism of dynamical filtering. Transmission device is finally designed on the basis of the maximal torque on the impeller shaft.