The invention provides a fuel full combustion method and system and belongs to the field of an internal combustion engine. Fuel in an oil tank enters an engine via a first oil conveying pipe for combustion; residual heat is discharged out of an exhausting flue; the first oil conveying pipe is arranged outside the exhausting flue; fuel in the first oil conveying pipe can be continuously heated by heat via the exhausting flue; during the heating, the fuel is converted from a liquid state to a gaseous state; fuel size is expanded after heating; then the fuel enters the engine and is fully mixed with air to release heat; and fuel in the first oil conveying pipe is continuously heated until the engine stops. The fuel is heated by the residual heat discharged by the exhausting flue expands after a conversion from the liquid state to the gaseous state; then the fuel is fully and evenly mixed with air, so the fuel can be fully burnt and release heat; with the above method, fuel utilization rate can be improved; obvious black material can be avoided in the inner wall of an exhausting port of the exhausting flue; and pollution to the environment can be reduced and the environment can be protected.