Abstract: The filling mining method is widely used in underground mining due to its advantages of disposing of a large amount of solid waste, controlling surface subsidence, and managing ground pressure. The flowability of the filling slurry not only affects its pipeline transportation, but also is closely related to its self-sufficiency and sealing performance in the empty area. This article uses slump and consistency tests to study the effects of thickener content and concentration changes on the flowability of filling slurry, and further analyzes the self-supporting and anti blocking and air leakage performance of thickened filling slurry. On this basis, industrial experiments were conducted on thickening paste filling corners to evaluate the filling effect of thickening paste. The results show that the 200 000 molecular weight hydroxypropyl methyl cellulose (200 000 HPMC) thickener can quickly dissolve in 10 seconds, meeting the needs of continuous filling operations. As the content of 200 000 HPMC increases, the slump and consistency of the filling slurry show a decreasing trend as a quadratic polynomial function. When the thickener content is constant, slightly increasing the concentration of the filling slurry will significantly reduce its fluidity and improve its self-sustaining ability inside the goaf. Based on the experimental results, considering the self-sufficiency and sealing function of the filling slurry in the goaf, the concentration of the filling slurry is 78%, and the effect is better when the content of 200 000 HPMC is 1 ‰ of the total solid mass. The industrial test results have confirmed that the recommended ratio parameters for preparing the filling slurry meet the requirements of self-sufficiency and sealing air leakage at the corner, and the CH₄ and CO concentrations decrease after corner filling. The research results can provide a reference basis for the thickening of filling slurry and the application of filling technology.