To obtain the pendulum parameter values under specified conditions, analogical analysis was used to derive the relation between shuttle length and liquid sloshing frequencies, and hypothesis and analogical analysis were combined to derive the relation between rod quality and liquid sloshing force. Then, FLUENT was utilized to simulate the liquid free oscillation under different original conditions, and the simulation results were used to draw the fitting functions of pendulum parameters about tank shapes and liquid fill levels. The roll moment obtained from FLUENT simulation and pendulum numerical computation has shown that the method proposed is quite useful and the relative errors between parameters fitting results and the actual ones are all in the range of ±4%.