An improved method of plane-wave time-domain algorithm (PWTD) of scalar field based on the present PWTD algorithm is presented. With this method, computation of interpolated function was transformed to tabulation of the interpolated function, and the maximum error was presented. Additionally the derivative operation in translation operator was placed on the outermost, which reduces original (K+1)(2K+1) times operation of FFT and IFFT to one time. Consequently the cost associated with the computation was decreased. Two examples were presented to demonstrate the accuracy and high efficiency of the improved algorithm.