Aimed at the problem that the process of modeling the net is complex and the relative errors between the gravity and buoyancy of the cables during the mesh grouping process reduce the accuracy of hydrodynamic performance evaluation, a modeling algorithm that unfolds the surface of the net is established. The method utilizes the modeling principle of unfolding the three-dimensional surface of the net into a two-dimensional surface and regulates the mesh grouping multiplier to control the modeling precision. In OrcaFlex, this algorithm is compared with relevant research results to verify the effectiveness of the numerical simulation and the algorithm. Based on this, under the conditions of pure flow and different mesh grouping multipliers, the numerical hydrodynamic simulations are carried out for the plane nets with different net depths and the cylindrical nets with different net diameters to derive the relevant linear fitting relationships for cable drag forces. The analysis reveals that the deeper the net depth and the larger the net diameter, i.e., the greater the number of mesh cells before grouping, the higher the sensitivity of the fitting function. According to the fitting function, the hydrodynamic drag values of the net before grouping can be obtained and the relative errors caused by the increase in grouping multiplier can be significantly reduced.