Abstract: In order to solve the problem of high cost of filling paste, sludge was used as aggregate to prepare filling paste. The orthogonal test method was adopted to carry out the proportion test of sludge paste filling materials, and the influence of sludge mass fraction, cement mass fraction and fly ash mass fraction on the slump, setting time and compressive strength of filling paste was discussed. On this basis, sludge mass fraction, cement mass fraction and fly ash mass fraction were taken as independent variables and the compressive strength of the filling paste was taken as the target value. Combined with response surface methodology (RSM), a prediction model for the compressive strength of the sludge filling paste was established to reveal the optimal ratio of sludge paste filling materials under multi-objective conditions. The results show that the strength of sludge filling paste is not only affected by single factor, but also significantly affected by the interaction among factors. The interaction between sludge mass percentage concentration and cement mass fraction is the key factor affecting the strength performance of filling paste. The optimized filling material ratio is as follows: the slurry mass fraction is 75%, and the lime mass fraction is 4%; the sludge mass fraction is 8.32%, and the cement mass fraction is 29.62%; the fly ash mass fraction is 20.33%. The test verifies that the compressive strength of the filling paste at all ages meets the design requirements under the ratio condition.