In this paper, an evaluation method based on the non-linearity degree of vibrating signals is proposed for the pedestal looseness of the sliding bearing-rotor system. The non-linear models for the sliding bearing – rotor system with and without pedestal looseness are established by means of such theories as rotor dynamics, mechanical vibration, and so on. The elastic force in the position of looseness fault is described by a non-linear term. In order to obtain the linear model for calculating the non-linear degree, the oil film force of sliding bearing in the non-linear dynamic model with pedestal looseness is linearized by means of eight dynamic coefficients, while the elastic force in the position of looseness fault is approximated by Taylor ex- pansion. The difference of dynamic behavior is compared between the non-linear models for the sliding beating-rotor system with and without pedestal looseness. The dynamic behavior non-linearity degree of the sliding bearing-rotor system under different loosening clearances is calculated by means of MATLAB numerical integration. The relationship between the non-linearity degree and the pedestal looseness is established, which will reflect the influence of pedestal looseness exerted on the dynamic behavior of the sliding bearing-rotor system and provide a new method for evaluating the pedestal looseness of the system.