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The paper tries to apply the Butterworth low-pass filter to inertial navigation system (INS) data processing. A set of INS heading data of a practical example has been calculated and the filtering tested. This filtering method is used to examine the correction of the results made by Guo and Wang. Based on the discrete Fourier transformation and the digital filter design technique, a Butterworth low-pass digital filter has been designed and performed to process INS heading raw data. The design of a special Butterworth filter includes determination of the technical specification of the filter and of the response function in the time domain or the frequency domain (determination of the order and cutoff frequency of the digital filter). For the high-frequency noise of INS raw data, a Butterworth low-pass filter has been designed to obtain a more accurate INS heading. The choice of the parameters and orders of the filter is also discussed in the paper. Finally, an example of INS heading data calculation is presented. The signal-processing TOOLBOX of MATLAB software is used for calculating and mapping the results. The result (RMS) is at the level of 0.01°. The method described here is simpler than Kalman filtering or the smoothing method and has sufficient accuracy for INS processing. It also provides ideas for some other series of raw data with high-frequency noise. [ABSTRACT FROM AUTHOR]