A compression-ignition low octane gasoline engine. The engine uses low octane gasoline and a compression-ignition method, does not require a spark plug, and compared with ordinary gasoline engines, increases thermal efficiency by approximately 40% and reduces green-house effects caused by emissions by approximately 45%. The “compression-ignition” of the low octane gasoline engine is a diffusion charge compression-ignition, differing from a homogeneous charge compression-ignition. The compression ratio in a cylinder can be 14 to 22, while an ordinary gasoline engine has a compression ratio of 7 to 11. The low octane gasoline engine has a simple structure, easy combustion control, a low noise level, and a low failure rate. As the low octane gasoline can be free of aromatic hydrocarbons, and not require the addition of antiknock agents such as MTBE and MMT, the present novel gasoline engine is a highly efficient, clean, and environmentally friendly internal combustion engine.