The paper presents a 12.8kbit/s LD-CELP speech coding algorithm that is based on the G.728 speech coding standard. The method can decrease effectively the size of vector quantization codebook by doing the statistical experiment of the codeword use frequency for codebook. The results show that the algorithm can hold better synthesis speech quality than other same type ways. And finally, the algorithm is implemented in duplex real-time on high speed DSP system with two TMS320C31s.