Clearances existing in artillery mechanism cause the muzzle disturbance and reduce the artillery firing accuracy. If the parameters of the clearance nonlinearity can be identified by taking advantage of the dynamic information, the quantitative relation between the clearance and muzzle disturbance can be established, and then the clearances of such nonlinear system can be controlled in a reasonable range to improve the artillery firing accuracy. This paper proposed a nonlinear identification method for the cantilever beam with clearances reduced from barrel-cradle structure. A modified restoring force surface method is proposed to identify the clearance value of the cantilever beam in time domain, and then a modified nonlinear identification through feedback of outputs method, i.e., reduced-order nonlinear identification through feedback of the output method, is proposed to recognize the related contact stiffness in frequency domain. The feasibility of the combined identification process is verified by a cantilever beam with two clearances in simulation, and a test-bed with adjusted clearance and contact stiffness which is regardless of other nonlinear factors by adjusting the position of the clearance and excitation method was designed to verify the effectiveness of this method. In the end, some influence factors of this identification process are discussed in detail. The results show that the proposed methods can identify clearance-nonlinearity parameters with high precision.