Abstract: According to some functions relation between the change of acoustic characteristic and the particle size of coal water mixture(CWM) when ultrasonic transmits in CWM,the paper put forward a design scheme of intelligent quick detector of particle size of CWM based on LPC2210 and uC/OS-Ⅱ,and applied PLL technology in the circuit of chronometry,so as to improve the measure precision of transmitting time of ultrasonic.The running result proved the detector is satisfied for requirement of particle size detection of CWM.