In this paper, a modified dynamic programming algorithm is adopted to improve the accuracy of the pitch detecting. It reduces the computation of the pitch detecting process and maintains the same performance of the classical dynamic programming algorithm at the same time. After the exact pitch is obained, the phase and amplitude of the glottal pulse during the voiced speech is employed to improve the naturalness and cleess of the synthesized speech. This algorithm produces natural and intellegent speech at 1200bit/s.