With the development of deep water oil and gas fields, subsea production system (SPS) has played an important role. Subsea process facility is in cold seawater environment. When the SPS is shut down, the oil in subsea manifold is prone to wax or solidify due to the cooling effect of the seawater. The method of wet insulation is adopted to achieve flow assurance of subsea manifold. During the cooldown time, the temperature of fluid shall be higher than the wax precipitation point and condensation point. Thermal analysis of subsea manifold is carried out for both steady state case and transient state case using OLGA software, and the thickness of wet insulating layer is figured out for the subsea manifold.