Abstract: In order to investigate the penetration rate improvement by implementing ultrasonic high-frequency rotary-percussive (UHFRP) drilling compared to conventional rotary drilling, as well as determining the influence of different drilling conditions and parameters on UHFRP rock breaking, we designed an ultrasonic vibration pup joint and built a test bench for ultrasonic rock breaking simulation. By using control variable method and orthogonal experiment method, we carried out a penetration rate enhancement test of ultrasonic rock breaking and the corresponding influencing-factor analysis tests. Thereby we obtained the influence law of weight on bit, ultrasonic amplitude, penetration rate, and bit diameter on the UHFRP rock breaking. The test results show that compared with conventional rotary rock breaking, the UHFRP drilling has higher efficiency of rock breaking at normal temperatures and pressures in the laboratory, with an average penetration rate increase of 77.65%. In addition, weight on bit, ultrasonic amplitude, bit diameter and penetration rate have a declining impact on the rock breaking efficiency of UHFRP drilling. Furthermore, weight on bit and ultrasonic amplitude have a highly significant effect on the efficiency of UHFRP rock breaking, and a larger amplitude results in a higher efficiency of rock breaking. The results show that the UHFRP drilling technology could provide a new rock breaking method in penetration rate enhancement of deep hard formations.