Abstract: This paper mainly investigates the application of the butterworth low pass digital filter in automatic measureing systems The necessity of applying the low-pass filter in those systems with high sampling rate and low output speed is discussed. In that way,the measurement noise can be decreased and the system resolution can be improved Compared with the conventional mult-point average filter, the butterworth filter has more satisfactory performances, and can be implemented with recursive algorithm, which needs less storage capacity of computer. The design method for determaining the parameters of butterworth low-pass digital filter is quite easy and convenient .The way for executing real -time filtering algorithm is provided, in which the high-order filter consists of several two- order filters in series and the first datum is used for repeatedly iterating many times, thus, the numerical instability is prevented successfully and the initial transient process is shortenedFinally, this paper gives a result of the application to the test of long-term gyro drift, which shows that the effect of low-pass digital filter is quite obvious. The signal of gyro drift with low-frequency property is truly conserved and the high-frequency noise from measurement circuit is basicly eliminated.