Abstract: This paper introduces an economical and simple experimental method to measure the onset sintering temperature of mixed coal ash. Under the pressure calculated from the formula , the ash with mass 3 g～5 g is compressed into ash bar in an Al2O3 tube with 8 mm～10 mm inner diameter. The pressure drop along with the ash bar versus temperature raised at a rate of 2 ℃/min～4 ℃/min temperature-increasing rate is measured with air flow rate at 10mL/min～40 mL/min. The onset sintering temperature of mixed coal ash is the temperature at which the pressure drop reaches maximum. The onset sintering temperatures of IHI CFB boiler ash and Qin Huangdao CFB boiler ash were measured. The onset sintering temperature of IHI CFB boiler ash is 900 ℃±10 ℃, which can partially explain the phenomena of the IHI CFB boiler can not run smoothly due to the sintering of ash and slag.