The liquefaction processes of mixed refrigerant cycle（MRC）and nitrogen expander cycle（N2 expander）for the special offshore associated-gas resources in South China Sea，have been designed and studied.The main performance parameters of these liquefaction processes have been compared at the same storage conditions and output of LNG.The layouts on LNG-FPSO for the two processes have also been compared and analyzed.The results reveal that the N2 expander is more suitable for offshore applications considering its many advantages such as simpler and more compact，more adaptable to the natural gases of different components，safer，and less sensitive to the motion of floating equipments，in spite of its shortcomings of higher power consumption and poorer economic performance.In addition，the exergy analysis is carried out for N2 expander.