The invention relates to a carbon-deposition-free engine. It consists of a cylinder block provided with a water-cooled cavity and at least two cylinder bores, each of which is fitted with a cylinder on the wall of the cylinder bore that is in contact with the cooling water or on the piston stroke section of the corresponding cylinder A certain number of grooves or through holes are opened on the casing wall. The invention can effectively reduce the high temperature inside the cylinder, maintain the lubricity of the cylinder, slow down the wear of parts, prolong the service life, prevent high-temperature sintering carbon deposition, make the cylinder in a more suitable thermal load state, facilitate the full combustion of fuel oil, and maintain strong power Output; the invention will not reduce the strength of the cylinder, and at the same time, due to the uneven thickness of the cylinder wall, the occurrence of resonance can be reduced, and the stability of the engine operation can be enhanced; the structure is simple, the cooling effect is good, the heat load of the piston and the cylinder liner is reduced, and the Reliable advantages, suitable for various types of water-cooled engines.