The utility model discloses a cylinder jacket fixed structure, including the cylinder block that is equipped with the mounting hole, install the cylinder jacket in the mounting hole, cylinder jacket upper portion is encircled and is equipped with ka tai, and the support shoulder -mounted in mounting hole upper portion setting is adorned to the card decometer, and the cover is equipped with the sealing washer between mounting hole and the cylinder jacket, thus the shaft part department between katai and sealing washer is equipped with clearance formation cooling sap cavity between mounting hole internal surface and the cylinder jacket surface, and the sealing washer setting is at the middle part of mounting hole or cylinder jacket, and cylinder block mounting hole internal surface is to cylinder jacket lower part location support. Make cylinder jacket and mounting hole lower part increase the fixed point through set up the location section in the cylinder jacket lower part with the chucking section, prevent that diesel engine operation in -process from producing too big vibration, and owing to be equipped with the gas -cooled chamber between location section and the mounting hole, hybrid oil gas passes through cooling channel entering gas -cooled chamber in the cylinder block to cooling cylinder jacket lower part reaches cooling and fixed balance.