Frequency, is to describe the frequency of periodic movement of the physical quantity, easy to transmit, anti-interference ability, many engineering measurements are related to frequency, such as sound frequency, mechanical vibration, measurement speed [1] .With the advance of the digital process, the traditional frequency-based circuit and timing circuit design of the frequency meter in the speed, accuracy and other aspects of the trend gradually, but was based on ultra-large-scale integrated circuit technology developed from the digital frequency meter to replace it on a large scale. Digital frequency meter can not only solve the problem of low efficiency of analog circuit information processing and transmission, but also improve the accuracy of frequency measurement [2] . Digital frequency meter is the use of digital circuits can be achieved on the cyclical changes in the signal frequency measurement of the instrument can be used to measure sine wave, rectangular wave, triangular wave and sharp pulse and other periodic signal frequency [3] .At present, there are many ways to measure the frequency of the frequency meter. Commonly used methods include interpolation method, cursor method, precision frequency measurement method, frequency difference multiplication method, phase comparison method, direct frequency measurement method and direct measurement method. Interpolation method and cursor method for analog circuits, the circuit design is complex, poor stability [4][5] . Frequency difference method is mainly used for frequency stability measurement, anti-jamming performance is poor [6] . Equal precision frequency measurement method is very high accuracy, fast operation, but most of its use of the chip is a programmable logic device, programming more complex [7] . Phase comparison method is mainly used for frequency accuracy and stability measurement, measurement accuracy by the hardware equipment constraints [8] . Based on the single-chip digital frequency meter commonly used frequency measurement method has direct frequency measurement method and direct measurement method, the direct measurement of the frequency range is limited, can only measure low frequency [9] . Direct frequency measurement is also limited by the frequency range, can only measure high frequency [10] . This paper designs a digital frequency meter based on C8051F020 single chip microcomputer. The frequency measurement method of digital frequency meter adopts the direct frequency measurement method and the direct