A novel method for estimating d-axis parameters of synchronous generators under d-axis load rejection test is presented.Firstly，new linear regression equations are constructed with q-axis voltage，excitation current and their numerical integrations.Secondly，coefficients of the regression equations are solved with measurement noises by an instrumental variable approach.Finally，the d-axis parameters are calculated from the estimated regression coefficients.The simulation results on a test case show that the proposed method has a better performance than the traditional response curve method or optimization modeling method.