Taking the production process of sludge-based biochar as the research object, based on the measured data of engineering field operation, the thermal balance models of sludge carbonization and cooling conveying system, pyrolysis gas incineration and waste heat recovery system, flue gas treatment and deodorization system were established respectively. The energy loss points in the process of operation were determined and calculated. The results show that the energy consumption loss of sludge-based biochar production process is 23550 MJ/h under the field operation conditions of feeding 2920 kg/h of dry sludge (moisture content 30 %), 19.65 kg/h of natural gas and 67 kg/h of fresh water, producing 1500 kg/h of sludge-based biochar (moisture content 4.5 %) and carbonization temperature 450 degrees C. Compared with the sludge drying incineration process, it can save energy and reduce consumption by 52.2 %, and the calorific value of sludge-based biochar is 7.04 MJ/kg, which is 49.6 % higher than that of dry sludge.