Aiming at nonlinear properties of landing gear oleo shock absorber and tire, a calculation method was presented to predict the natural frequencies of rigid body fuselage free vibrations on elastic landing gears from equivalent linear model. Application of oleo shock absorber and tire equivalent stiffness and damping test data, an iterative procedure was utilized to solve the fuselage natural frequencies. The various effects such as helicopter gross weight, rotor lift, ship motion state and wind ship-borne to natural frequencies were analyzed. For the fuselage second lateral mode, which is the least stable fuselage mode, its natural frequency is the lowest for the case of maximum gross weight with high rotor lift. In such a case the stability margin of rotary revolution will be reduced about 133r/min compared to the case of minimum gross weight with zero rotor lift. All types of ship motion state and wind ship-borne hypotheses in this paper had hardly effects to fuselage natural frequencies. A simpdecoupling model, independent in fuselage longitudinal-pitch and lateral-roll motions, showed enough precisions in natural frequency predictions.