Abstract: In geodesy many models are nonlinear ones. The classical method dealing with these nonlinear models is linear approximation using the approximate value of parameter. Due to the difference of nonlinearity between different nonlinear models, some nonlinear models can be linear approximation and the others can not be. To judge a nonlinear model can or cannot be linearized, reference1 has presented a criterion. Based on reference1 this paper defines interinsic nonlinearity and parameter effects nontinerarity of a nonlinear model at first. Then according to the definition a new practical criterion has been presented. The new practical criterion not only has the characteristic of the criterion in reference1, but also overcomes the defect of the criterion in reference1. Compared with the criterion in reference1 the new one has many new characteristics.