The pressure relief check valve plays a pivotal role in determining the oil and gas content during deep in-situ pressure-preserved coring. Prolonged exposure to high-pressure, high-solid-content fluids in deep wells can lead to mechanical erosion of the check valve, potentially causing severe failure and a loss of sealing integrity. To withstand the typical flow conditions in shale gas wells and on the basis of an in-depth understanding of deep fluid dynamics, a check valve was designed to operate at 70 MPa pressure and relieve pressure after coring. To mitigate erosion, a coupled Computational Fluid Dynamics-Discrete Element Method model was applied to simulate fluid flow dynamics and identify regions susceptible to erosion and wear in the valve body. The findings confirmed that the proposed check valve design meets the requirements for shale gas pressure-preserved coring and testing, with erosion mainly occurring in the constricted regions of the flow path. The erosion depth was found to increase with higher inlet flow rate and mass flow rates, demonstrating a sixfold increase as the inlet flow rate rises from 10 to 30 m/s. Non-spherical particles caused significantly more erosion than spherical ones, while the erosion depth decreased with larger particle sizes, showing a 33% reduction as particle size increased from 0.02 to 0.14 mm. To avoid sealing failures caused by prolonged erosion, the constricted flow channel was redesigned to accommodate an arc-shaped structure and appropriately widened. Simulations indicated that this structure can reduce peak pressure to 69% of the original value and minimize wall impacts. The maximum erosion depth decreased by 10%, indicating the improved durability and sealing of the redesigned check valve. These results underscore the enhanced check valve’s superior erosion resistance and sealing performance, highlighting its potential for future shale gas collection and testing and providing an effective strategy to enhance the reliability and longevity of check valves.