On account of the test condition of measuring the automation motion law，the data of test included some high frequency noisy need to be eliminated.The principle of the methods of smoothing data，such as moving average smoothing，locally weighted scatter plot smoothing and locally weighted robust scatter plot smoothing were discussed.And the data was simulated using the methods with different points.At the same time，the simu-lated data were compared with the result of differentiation directly，contrasted to the velocity curve of the firearms'automation which calculating by the testing system with higher precision.Finally the reasonable smoothing method is concluded from the result of comparison.