Abstract: Experimental tests were carried out to a 1 060 t/h circulating fluidized bed (CFB) boiler with breeches-leg under different operation conditions, after which the curves of in-furnace pressure distribution and the particle concentration distribution in the dilute region were obtained at different loads. Meanwhile, the impact of air velocity and pressure drop on the particle concentration distribution was analyzed, and subsequently the variation laws of particle concentration distribution, respectively with air velocity and furnace height, and with pressure drop and furnace height, were obtained. Results show that at a steady pressure drop, the air velocity is directly proportional to the average in-furnace particle concentration; whereas at a steady air velocity, the pressure drop is directly proportional to the average particle concentration in a certain range; when the bed pressure rises to a critical value, the pressure drop is inversely proportional to the average particle concentration in the furnace.