The evaluation of time-domain impedance matrix elements needs to respectively compute the space-time integrals in the field cell and the source cell.Because of temporal basis function’s regionality and its derivative’s uncontinuity(such as the triangle temporal basis function )

the accuracy of space-time integral in the source cell is worse by method of the gauss integral and the error increases when time interval gets narrow.The paper accurately computes time-domain impedance matrix elements by transforming space-time integral of the source cell to 1D time convolution and 1D space analytical integral and further solves time-domain electric field

magnetic field and combined field integral equations by method of marching-on-in-time.Numerical results show that the proposed method insures that the solution of time-domain integral equation using marching-on-in-time method is stable and accurate when the time interval changes in the broad range.