To solve the problem of the equivalent load conversion of the plane rotating mechanism driven by the hydraulic cylinder, the equivalent mass and equivalent viscous damping coefficient calculation formulas were derived by using the equivalent moment method, and the AMESim simulation platform was used to model and simulate the plane rotating mechanism driven by the hydraulic cylinder. Compared the theoretical calculation results of the hydraulic natural frequency and damping ratio of the equivalent system with the simulation results, the rationality of the equivalent mass and equivalent viscous damping coefficient calculation formulas obtained by theoretical analysis was proved. The proposed equivalent load conversion method is also suitable for the planar rotating mechanism driven by pneumatic or electric cylinder.