Aiming at the problem of the traditional catapult mechanism of aircraft missile, a hydraulic catapult mechanism with an accumulator providing catapult flow and a servo valve as the core control element was designed. The operating principle of the hydraulic catapult mechanism was discussed, and its simulation model was established by using AMESim software. The simulation results show that in the process of catapult, the volume of the accumulator gas chamber and the area of the piston at the rodless end of the hydraulic cylinder are positively correlated with the extension velocity of the hydraulic rod, and the area of the piston at the rodend of the hydraulic cylinder is negatively correlated with the extension velocity of the hydraulic rod; in the process of buffering, the end velocity of the piston rod and the pressure of the buffering chamber are negatively correlated with the clearance between the flange front end and the piston inner chamber wall.