Abstract: A new mechanism of saving energy and reducing pollution is brought forward by analyzing water characters and all factors which bring saving energy and reducing pollution in the combustion process of emulsification oil. The theory shows that the reason of saving energy and reducing pollution is that emulsification oil can reduce surplus air ratio effectively. By this new theory, the reason of saving energy and reducing pollution in the combustion process of emulsification gasoline, emulsification diesel oil and emulsification heavy oil of W/O or O/W can be well explained, especially for that in a boiler with favorable combustion state. According to the theory, a good performace of the high soften-point pitch-water slurry combustion is gained.