Abstract: In this paper the servomotor systems are studied.A new method is proposed in which the dynamic parameters of servomotor systems with their changing state are identified by means of least square method with moving range. In the proposed method the nonlinear parameters are identified by the calculation method of step-by-step identification and approach on the bsasis of theorem and methods of linear parameter estimations.The main points are summarized in the following:(1)A scheme suggests that the length of moving range is set up in accordance with a period of identification input signal.(2)After the corresponding relations between parameters and states are ientified by least mean square method with moving range,each parameter which is changed depending on states is identified for getting the models of non-linear parameters.(3)The non-linear model of a servomotor can be obtained by substituting models of nonlinear parameters. The approximate model of a non-linear servomotor is confirmed through W examination of identification errors.This approximate model has higher precision than the linear one