Fresnel ultrasonic lenses with different focal lengths are designed.The visualization of 40 KHz ultrasonic field distribution passing through a Fresnel ultrasonic lens is realized by using VSchlieren optical path.According to the collimation of sound field distribution after passing through Fresnel ultrasonic lens,the focal length of acoustic lens can be measured in the visualization state like the traditional experiment of measuring the optical focal length.The measurement results of the focal length of acoustic lens by using the experimental device are in well agreement with the design values.The acoustic measurement is completed by optical means,and the combination of optical and acoustic content in college physics experiment is realized.