Offshore oil and gas exploration forward deepwater and ultra-deepwater, due to marine engineering pool limitation, it is very difficult to use conventional reduced scale do full-depth system model test, so hybrid model test techniques are used and equivalent truncation design is required. The truncated mooring system mathematical model is mainly designed based on static characteristics similar criteria, writing the single mooring line nonlinear equations of static equilibrium algorithms, to get single mooring line tension and mooring system restoring force, choosing the objective function appropriately, various parameters of truncated mooring system are designed by using Genetic Algorithm through programming software MATLAB. The results calculated by the developed program are compared with the hydrodynamic calculation software Orca Flex, to check the accuracy. Based on the designed parameters, the truncated mooring line top tension-displacement curve and system restoring force curve are drawn by using the developed program, and compared with the full-depth system. Hydrodynamic calculation software AQWA is applied to calculate the dynamic characteristic difference between the two systems. A turret moored FPSO of 1500m water depth is as an example to make the equivalent truncated optimization design of 700m. The results show that the developed program is feasible.