Abstract: Aiming at the engineering problems of strong jet impact, severe vibration and high operation safety risk caused by direct blowdown of high-pressure fluid inside casing after cementing displacement bump pressure of shale gas horizontal wells, a two-stage cyclone pressure relief buffer device for cementing was developed based on Navier-Stokes equations and fluid kinetic energy gradient dissipation mechanism. The device guides high-pressure fluid tangentially to form forced vortex in the primary buffer chamber to convert axial kinetic energy into rotational kinetic energy. The parallel structure of symmetrical double secondary buffer chambers greatly expands the total outlet flow area to realize square-order attenuation of flow velocity, and the reverse torque of symmetrical chambers counteracts each other to ensure stable operation of the device. Standard κ-ε turbulence simulation coupled with Schnerr-Sauer cavitation erosion numerical simulation was carried out by SolidWorks Flow Simulation software, and performance verification was completed combining indoor displacement test and field application in shale gas wells. The simulation results show that under 60 MPa high-pressure working condition, the fluid inlet flow velocity is 350 m/s, and the outlet flow velocity drops to 10 m/s after two-stage buffering, accounting for only 2.86% of the inlet flow velocity. The high erosion risk area is concentrated on the wall facing the jet in the primary buffer chamber. 35CrMo steel can meet the long-term service requirements, and surface strengthening coating can further improve the erosion resistance of severely worn areas. Indoor tests demonstrate that fluid impact can be reduced by more than 80% under 2 m³/min displacement. Field application in Fuling shale gas wells of Chongqing verifies that the blowdown lasts for 30 s under 58 MPa wellhead pressure, the fluid impact is obviously weakened, and the jet diffusion range is controlled within 1 m². The wall thickness wear is only 0.1 mm after cumulative application in 50 wells, and the erosion resistance meets the design requirements. Relying on staged cyclone to dissipate fluid kinetic energy, the device can greatly reduce the fluid flow velocity and field safety risks during cementing pressure relief, providing reliable supporting equipment for high-pressure cementing blowdown operation of shale gas horizontal wells.