Abstract: For analyzing the influence of gear pair vibration on simulation results of trapped oil pressure stored in the two trapped oil zones of external gear pump, the related pressure simulation model was derived, based on vibration and vibrationless of gear pair, the various leakages from the two trapped oil zones were compared with each other, then the size of two trapped oil pressure value was theoretically analyzed, and the analyzed conclusions were supported by simulation results and experimental verification. All results showed that the pressure peak in the first trapped oil zone was greater than in the second trapped oil zone; the peak difference of two trapped oil pressures in the case of vibration was smaller than in the case of vibrationless; the higher output pressure of pump was, the greater peak difference was; and the simulation results in vibration was more accurate than in vibrationless, for example, the simulation error of the sixth group was reduced from 16.7% to 7.8%, thus in the simulation of trapped oil pressure, the vibration factor was necessary to be involved, et al.The dynamic trapped oil model can provide a theory and for next pump design