Ultrasound (US) imaging is a non-invasion and non-radiation medical imaging system. One of them, the single-element transducer has significant potential in the medical device. As compared to an array transducer, it could reduce the size of the imaging system. For example, the ultrasound needle for epidural anesthesia and eyeball. In this study, we develop a free-hand US system on skin imaging. Using the 20 MHz high-frequency single element ultrasound transducer on the skin scanning. The high-frequency ultrasound could provide an excellent resolution to 0.1 mm. The bandwidth of the transducer is 20%, and the Insertion loss (IL) is –31.9 dB, and the Electromechanical coupling factor (Kt) is 0.72. Meanwhile, the free-hand apparatus which based on the optical tracking sensor is designed and applied in this system. It is convenient for scanning the skin surface. This control and display panel is designed by the LabVIEW software. The in-board filter and Hilbert transformation are used to eliminate the environment noise. To solve the problem of unstable scanning speed, the interpolation method with one order is used to fit and smooth the image. Therefore, the high-quality ultrasound images could be applied in the skin scanning.