This paper schemed out an ophthalmic high frequency A-scan ultrasonic instrument to measure corneal thickness and ocular axial length, using pulse reflection principle and double counting method. A special ultrasonic high frequency transducer was designed to get higher resolution. In addition, differential circuit reduced the pulse width, thus improved the accuracy. From the results of comparative experiments with Orbscan II and general A-ultrasonic instrument, the device achieved its good goals.