Abstract: This study aimed to develop a predictive model for the separation efficiency of a hydrocyclone-based sand separator based on boundary layer theory. Numerical simulations were first employed to calibrate the effective flow rate and effective retention volume of the hydrocyclone, resulting in a formula for calculating residence time. The study then analyzed the forces acting on solid particles in the boundary layer, considering the influence of velocity gradients on particle forces, and derived a radial motion differential equation suitable for the hydrocyclone. Based on these adjustments, a refined separation model for the hydrocyclone was established. Experimental validation results indicate that, for particles larger than 13 μm, the model achieves a relative error of 12%, significantly lower than the 46. 5% error predicted by traditional boundary layer theory. This outcome demonstrates a closer alignment with experimental data, offering more precise parameter support for engineering design.