The structural dynamic characteristic of all-terrain vehicle (ATV) affects greatly its vibration performance and riding comfort, but a simple, common and effective finite-element modeling method for ATV frame with an elastically mounted engine is rare. Based on simulation and test for ATV body, a simple and common finite-element modeling method was proposed which simplified the engine as a meshed cuboid structure with same centroid, weight and rotary inertia to the engine and linked engine to MPCs fixed on the frame through SPRING elements. Considering nonlinear changes of elastic engine suspension stiffness in different operating conditions, the influences of the proposed modeling method on the structural dynamic characteristic of ATV body under different elastic engine suspension stiffness were studied. The results show that finite-element modeling method for ATV frame elastically connected with engine meets the engineering requirements. This simple and common modeling method is useful to know the structural dynamic characteristic of ATV frame elastically connected with engine in the phase of product design and retrofit which could applied in developing and design the ATV with an elastic engine suspension