Abstract: To improve the rock-breaking efficiency of PDC bits and reduce stick-slip vibration, a compound axial and torsional impact tool was developed. This tool, characterized by a simple structure and the synchronous action of axial and torsional impacts, is used to break rocks. To do so, it used a self-excited oscillation pulse jet as its energy source, and converted axial impact force into compound axial and torsional impacts through helical surface structure. Field applications showed that: compared with conventional drilling tools, the ROP of this compound axial and torsional impact tool was increased by 95.2%–193.8%, and the footage of a single bit was increased by 46.4%–229.2%. Compared with PDM drills, the ROP of this tool was increased by 71.0% while compared with axial impact tools, the ROP of this tool was increased by 66.3%, and the footage of a single bit was increased by 194.0%. Compared with torsional impact tools, the ROP of this tool was increased by 30.2%–46.8%, and the footage of a single bit was increased by 17.2%–191.8%. The research results showed that the developed compound axial and torsional impact tool can improve rock-breaking efficiency and reduce the stick-slip vibration in hard formations. With its remarkable rock-breaking effects and ROP improvement, this tool is worth of application and widespread implementation.