In this paper, systematic experimental investigation on the heat flux distribution inside the furnace of a 300 MW CFB boiler was presented. Detailed experimental setup and measurement techniques were presented and a finite element method approach was applied to determine the heat flux. The heat flux profile on the rear wall along the horizontal direction shows a significant imbalance at different boiler loads. As a result of the non-uniform layout of the heating surfaces, which is the essential reason, as well as the imbalance and deviation of the temperature field, solid suspension density and solid flow rate, the central section of the furnace possesses higher heat flux distribution compared to the side sections. The heat flux is also found to increase with the increasing boiler load and decrease as the height increases. Heat flux near the roof, where the solid suspension density is rather small, is found to decrease remarkably revealing less heat absorption in this area. In addition, an empirical model of heat transfer coefficient is revised using the average data at different boiler loads. A mechanism heat transfer model based on the membrane water-wall configuration is proposed and validated with the heat flux profile obtained from the measurement. The model provides good accuracy for correlating 85% of the data within 10%. (C) 2013 Elsevier B.V. All rights reserved.