Abstract: We propose a new method where systematical errors are involved in observation equation.Because the number of observation equations are less than that of unknown parameters,observation equations are rank-deficient.With ambiguity resolution,based on "select weight fitting" principle,observation equations are constrained not only through baseline components but also through systematical errors continuations of adjacent epochs.According to this method,the impact of systematical errors on GPS DD positioning accuracy can be mitigated effectively.Furthermore,the systematical errors can be achieved directly.