In the real quantum key distribution (QKD) system, statistical fluctuation of the source parameters will happen with the changes of time and environment, which will lead to a serve decrease of the key rate. Regarding to the problem, a method is proposed to eliminate the influence of statistical fluctuation of the source parameters on the performance of QKD. In the method, the heralded coherent sources are used to replace the widely used weak coherent sources, which can significantly improve the key rate of QKD when there is statistical fluctuation on the source parameters, and thus the influence of statistical fluctuation on the source parameters is eliminated, while the maximum transmission distance is also significantly improved. Both the theoretical analysis and numerical simulation verify the feasibility of the proposed method, and it is believed that the method can provide a new idea for the practical application of QKD.