BPA and Matpower toolkit based on MATLAB are two kinds of software which are most used in China. In order to realize the fast and accurate large-scale power flow calculation and power system analysis on MATLAB platform, After analyzing the characteristics of BPA data structure in detail and the characteristics of Matpower data structure, A interface program which is fast and accurate in separation and conversion of data is designed. Through the analysis of detailed BPA data of Guizhou power grid, We compared the results of two kind of data network for power flow calculation, Indicating the utility, accuracy and effectiveness of the conversion interface program and the reason for the error is explained.