The detailed BPA grid data of each province grid, and the important component package Matpower in Matlab software can be utilized to fulfill rapid and accurate flow calculation and power system analysis. On the basis, adopt the Matpower to make rapid flow calculation on Matlab platform, and aimed at the non-compatibility problems of BPA data and Matpower existed during the calculation, a data interface based on BPA-Matpower is designed. The data construction of BPA and Matpower were analyzed, and based on which, the transformation principle of BPA-Matpower data interface was discussed, including the corresponding relationship between BPA and Matpower data construction, and the transformation flow chart of BPA-Matpower data interface. Based on the BPA data of one certain city grid, an accurate example was given, which shows that the designed BPA-Matpower data interface can achieve data transformation from BPA data to Matpower data, thus solves the non-compatibility problems of BPA and Matpower data.