Optical gradient force, as a novel type of actuation force for nano-resonators, has recently attracted a lot of attention. In this paper, the inherent nonlinear characteristics of the optical gradient force are analyzed. A nonlinear dynamic model of the ring and spoke resonant system driven by optical gradient force is proposed. The influences of optical input power and geometric parameters on the nonlinear dynamic responses of the system are investigated. The results show that the optical gradient force can cause stiffness to soften. The amplitude increases and the resonance frequency shifts as the input optical power increases. Moreover, the amplitude and resonance frequency of the nano-resonator decrease as the initial gap of the rings increases. Therefore, the resonance frequency can be adjusted by changing the optical input power. This work can be useful for the further design and performance prediction of nano-resonators driven by the optical gradient force.