Beginning with a detailed introduction of CS-ACELP algorithm based on G.729 protocol,this paper does analysis of the algorithm's computational complexity of each functional modules,which shows high complexity and high demanding for the hardware system.Thus some improvements are made by reducing the impulse locations and adding general search in the low correlation impulse locations,which can accelerate the fixed codebook search and reduce the computational complexity.Experiment simulation is carried out to verify the feasibility and effectiveness of the improved algorithm.