Abstract: In order to explore the two key parameters of "hydraulic slope" and "critical flow rate" in the design of in-situ filling pipeline system, the existing hydraulic slope and critical flow rate models were modified. Taking A material as the research object, indoor hydraulic experiments were conducted to investigate the actual hydraulic slope and critical flow rate of A material slurry under different inclination angles and mass concentrations. The parameters were estimated and the accuracy of the model was explored, the engineering inspection was conducted based on the in-situ filling of the 7105 old roadway in a coal mine in the southwestern region of Shandong. The research results showed that: (1) as the inclination angle increases, the hydraulic slope gradually increases, and the inclination angle influence coefficient α The approximate linear relationship with the inclination angle of the pipeline; The near flow velocity is influenced by both the inclination angle and concentration, and the higher the concentration and inclination angle, the greater the critical flow velocity. (2) Obtained from experimental data α、β fitting the formula and incorporating it into the correction model, the error of the hydraulic slope model results is within 10%, and the error of the critical flow velocity is within 5%; (3) The on-site filling pipeline system designed based on two key parameters is unobstructed, and there is no siltation or severe wear of the pipeline, proving the feasibility of the values of hydraulic slope and critical flow rate in practical applications.