In this paper, we discuss the accuracy evaluation methods of guidance system and analyse a varieties of factors of affecting guidance accuracy. On the base of qualitative analysis, the error model of guidance system was established and was inducted to linear regression model. In the end, analysing and comparing many error detachment methods used at prescnt, the model reference adaptive generalized ridge estimation method is presented by model reference adaptive thought in combination with ridge estimation method. A efficient way is presented to solve the problem of guidance system error detachment.