Because of complexity related to operation, maintenance, support and malfunction of ship steam power system, establishing math analytical model cannot satisfy the RMS argumentation demand. Based on the minimal equipment listing, Monte Carlo simulation method is not fit for system failure criterion either. The current research utilized feasible using schemes based on thermal model instead of minimal equipment listing based on logic relation. According to whether there were feasible using schemes when system partial equipment faulted, the research designed ship thermal system RMS simulation flow based on feasible using schemes. The ship thermal system RMS software was programmed based on improved simulation flow. Calculation examples demonstrated that the improved flow can satisfy the simulation precision, and the calculation efficiency is also improved.