Abstract: Development of hydraulic punch while drilling, solves the problem that the hydraulic punch is required to insert after the drilling hole is finished in hydraulic punching construction in underground coal mine .Good results have been obtained in the drilling of the upward penetration layer hole. But in a near horizontal or lower oblique hole, Drilling slag is difficult to drain from hole with drilling fluid due to the gravity effect of drilling slag, which cause hole collapse accidents. In this paper, hydromechanical analysis is carried out on hydraulic punching construction process, and the loss the hole, the pressure of puncher hydraulic reversing valve and the flow rate of driling fluid needed was calculated. By adding water jets at the bottom, Increase the flow quantity of punching and the upstream flow rate of drilling fluid, So as to solve the problem of slag discharge difficulty. According to the improved hydraulic parameters, the reset spring of the punch was redesigned. The filed test was carried out which the improved hydraulic punch was used, tests show that the direction-change valve of the improved hydraulic punch works stably.Drilling slag can be discharged out of the hole in the near horizontal oblique borehole,which meets the requirement of hydraulic punching construction in under inclined borehole in coal seam.