Abstract: The A-type pulse reflection ultrasonic instrument is used to measure the sound path in liquid level of the hydrophobic pipe.The liquid level is obtained by calculation and the calculation results are corrected by formulas.It is achieved in the measurement of the liquid level of the hydrophobic pipeline conveniently and efficiently in the range of 20℃ to 60℃,using the A-type pulse reflection ultrasonic instrument. The error of the detection result calculated is ±1 mm.