Abstract: In order to improve the full-flow state of backfilling pipelines in deep mines, full-flow ratio was put forward to regard as a quantitative index to describe the full-flow state of the filling system. At the same time a mathematical model of full-flow ratio was deduced based on the hydraulic transmission theory and its influence factors were also analysed in theory by using the mathematical model. It is found that reducing the pipe diameter or increasing the slurry flow velocity is the best way to increase the full-flow ratio. On the basis of the pipe two-phase flow theory, a mathematical expression about the relationship of the pipe diameter, velocity, and full-flow ratio was also established, which provides a theoretical basis of selecting the best conveying parameters for the filling system. A local reform, replacing Ф150 mm pipes with Ф85 mm pipes and increasing the flux to 80 m³·h^-1 simultaneously, was carried out in a deep mine filling system. The results show that the full-flow ratio of such system is able to be improved by 6 times and the pipe wearing can be reduced effectively.