The invention discloses a piston reciprocating type single-cylinder low-speed internal combustion engine adopting a gear-rack mechanism in a first embodiment of the Chinese invention patent with the patent number of ZL200710147446.7 and the publication patent number of CN101144524B as a power mechanism. The piston reciprocating type single-cylinder low-speed internal combustion engine is composed of the power mechanism, the product of the Chinese invention patent with the patent number of ZL200710193938.X and the publication patent number of CN101289956B, the product of the Chinese invention patent with the patent number of ZL200710193940.7 and the publication patent number of 101205861B, the product of the Chinese invention patent with the patent number of ZL200810169739.X and the publication patent number of 101434419B, the product of the Chinese invention patent with the patent number of ZL201112083190.9 and the publication patent number of CN102562339B, the product of the invention application with the application number of 200710193939.4, the product of the invention application with the application number of 201310434603.X, the product of the invention application with the application number of 201410020453, and the product of the invention application with the application number of 201410208643.5. By the adoption of the engine, the disadvantages and defects of an existing conventional internal combustion engine can be comprehensively overcome, and the piston reciprocating type single-cylinder low-speed internal combustion engine has the positive effects that the heat efficiency is about 70%, the specific weight is relatively reduced by about 30 times, and emission of various harmful combustion pollutants to the atmosphere is basically eliminated.