Abstract: According to the abnormal high exhaust temperature of water jacket heater in a gas reverse transmission project, field survey and sampling analysis of composition of ash deposition are carried out. This paper points out that the main reason causing the high temperature is inadequate combustion of the fuel, which leads to ash deposition polluting the heating surface of smoke tube, and then reduces the flue gas's heat transfer capacity on working fluid. The water jacket furnace is disassembled in order to study the mechanism of ash deposition on smoke tube and analyze its process. Then preventive measures for high exhaust temperature and suggestions on safe operation and maintenance of water jacket furnace are proposed.