Abstract: The structure and the functions of the high-speed FX correlator of Chinese VLBI network are described, and its long term accumulator (LTA)is introduced in detail.The long term accumulator is the data reduction module of the correlator.Enhancing the integration of the circuit and the reliability of LTA, an improvement is presented by means of the study on the long term accumulator, to meet the new requirements for the correlator, such as higher speed and higher precision.Meanwhile, a specific way to implement the improvement and its traits after the improvement are introduced briefly.