After the size of the instrument to test the flow resistance is reduced from large to small, its tight arrangement leads to the signal interference of the electronic components and the airflow fluctuation of the equipment is large in the equipment. This phenomenon causes the stability of the test system to deteriorate. Through the diagnosis of interference causes, the simple filtering method makes the test accuracy poor. Through the summary of various problems. Firstly, the median algorithm is used to eliminate the pulse signal. Then the recursive averaging algorithm is used to eliminate the periodic variation of the intake system and the vibration interference of the vacuum pump. Furthermore，the mean absolute error and mean square error are used to define the optimal value of the algorithm. Finally, the data distortion before low-pass filter processing will be reduced. The experimental results show that the test system using the improved median recursion method has better stability, but its response speed is slow. The improved median recursion method can effectively eliminate the interference signals of periodicity, pulse and dither. The static testing system that it applies to has high requirements for testing stability and testing progress, but low requirements for real-time testing.