Based on the pipeline stress analysis software CAESAR II, a FPSO project is taken as an example to study the analysis method of deck cargo offloading system. The impact of various loads such as wind, hull acceleration, sagging and hogging, and blast resistance force on piping stress is given and the load calculation is described in detail. The difference between the method of combined load case and independent load case is analyzed. According to the actual operation condition and load situation under design operation case, extreme design case and blast case, the method of combined load case is used to perform the static analysis and fatigue analysis, which guarantees the safety of piping system in given condition and provides reference for FPSO hull piping stress analysis.