Abstract: Single-frequency GPS ambiguity resolution on-the-fly has the problem that normal equation is ill-posed. Using epoch-differenced coordinate information between neighboring epochs can mitigate the ill-condition problem to some extent, as a result, the accuracy of the float ambiguity solution will be improved and the convergence time of ambiguity will be shortened. In order to further improve the ambiguity fixing effciency of epoch-differenced method, the epoch-differenced coordinate pseudo-observation error equation and its new variance matrix is reconstructed. The experimental results show that, compared with the previous algorithm with epoch-differenced coordinate information, the new method has higher stability and efficiency.