The invention discloses a method for soft measurement of the 
smoke temperature of an outlet of a 
hearth based on the real-time slagging condition of the 
hearth to overcome the defects of an existing method for soft measurement of the 
smoke temperature of the outlet of the 
hearth. According to the method, the real-time slagging condition of the hearth is reflected through the heat effective coefficient of the water-cooled furnace wall during soft measurement of the 
smoke temperature, and the real-time changeability of the real-time slagging condition of the hearth is calculated and considered; a calculation output part mainly includes calculation of comprehensive 
heat transfer of the hearth and part of a 
convection heating surface and output of the heat effective coefficient of the water-cooled furnace wall and the smoke temperature of the outlet of the hearth; on the basis that the number of measurement points of a boiler is not increased, the quality parameter and the structure parameter of 
coal placed into the boiler and the real-time operation parameter of the boiler are collected, a model for real-time calculation and soft measurement of the smoke temperature of the outlet of the hearth is established by combining the 
heat transfer balance calculation of the hearth with the 
heat transfer balance calculation of the 
convection heating surface and considering the real-time slagging condition in the hearth; a real-time value of the smoke temperature of the outlet of the hearth can be output, the real-time slagging condition in the hearth can be provided, and the real time value of the smoke temperature of the outlet of the hearth and the real-time slagging condition in the hearth can serve as visual data references for conducting hearth ash blowing and water desuperheating of the high-temperature heating surface by operating personnel.