Abstract: Reciprocating engine is also called piston engine, and it is the machine which transforms thermal energy from burnt fuel into mechanical energy through one or more pistons. Reciprocating engine is mainly consisted of crank connecting link, admission gear, fuel feeding system, lubricating system, refrigerating system, ignition system and starting system etc. Operating principle of the engine is presented. The work cycle which consists of air admission, compression, applying work and air exhaust is constantly repeated, so the transformation from thermal energy into mechanical energy is implemented, and the engine is under continuous operation. Reciprocating engine can be worked in efficiency and be prone to field maintenance, and its output power is less sensitivity to altitude and ambient temperature. So in driving oil pump reciprocating engine is more preponderant than gas turbine. Reciprocating engine in the oil pump driving will be widely applied with the rapid development of world pipeline industry.