The purpose of this paper is to investigate subsea processing system on how to impact on flow assurance, and to propose some design methods about subsea system. The paper discusses the subsea processing system on how to relieve the hydrate and decrease usage of hydrate inhibitor, to increase the tie-back distance, to improve production rates and increase total recovery. The study analyzes the differences of effect on flow assurance whether with or without the subsea processing system. The design principle of subsea processing system is researched, such as, how to get the optimum location for the deepwater subsea processing system, boosting pump selection, subsea processing compared with topside processing, the efficiency of subsea processing system, process flow design of subsea processing system. In addition, the subsea processing system is simulated with dynamical flow software. The purpose of dynamic simulation is to determine the control strategy and operation philosophy of the subsea processing system. The flow is modeled with the dynamic multiphase flow simulator OLGA.