Abstract: To optimize the mixture ratio of gangue paste filling for Daizhuang Coal Mine, firstly, 28 groups of experiments were carried out by using uniform design to study the influence of different mixture ratio on slump, layering degree, bleeding rate, early strength and long term strength of paste. Then, a calculation formula for the long term strength of paste was proposed according to the theory of key strata. Moreover, the filling performance parameters were fitted by Matlab software. At last, the optimal mixture ratio is that the ratio of fly ash to cement is 3.2, the ratio of broken gangue to cement is 4.5 and slurry concentration of paste is 75.3%. Under these conditions, the results of filling performance parameters are slump of 184.44 mm, layering degree of 13.87 mm, bleeding rate of 1.48 mm, 0.16 MPa and 3.89 MPa of early strength and long term strength of paste respectively, which are agreement with the experimental results.