Percussion drilling has been widely used in oil and gas exploration, while there are still some problems, such as severe damages to drilling tools, low energy transfer efficiency. The energy transfer and rate of penetration are key parameters of the percussion drilling. According to the practical application of the percussion drilling, the calculation assumptions, establish the three-dimensional model, define the material properties and element types, meshing, define the contact, apply load are described. The finite element model of that the geophysical prospecting impactor-bit-rock interaction was established. The computer simulation was finished. The results indicate that: the energy transfer efficiency when the impactor piston impacted bit is 73.0%. The depth of that the bit broke the rock is 6.4 mm in one percussion-rotary drill. The impactor piston had radial velocity and displacement during the motion process. Its harm is very big. It should be reduced as much as possible. The results are further useful to extend the applications of the geophysical prospecting impactor and hammer bit.