The hydraulic system with a long pipe on offshore drilling platform was studied. The timedomain response of the system was analyzed by building a simplified mathematical model. The offshore hydraulic system was modeled based on AMESim, which offered an effective method to analyze its dynamic characteristics through the system response curves under different parameters, such as pipes length，diameter and oils viscosity，elasticity modulus. The effect of the accumulators position to the system dynamics was also analyzed. The impact of every single factor on system dynamic performance was analyzed based on RSM and the system was optimized. The optimized results improve the response time 349% of the original design. It can be used as reference in future design of offshore hydraulic system with long pipe.