When optical time domain reflectometer(OTDR) uses small pulse width test, its curve signal-to-noise ratio is low and dynamic is insufficient. If large pulse width test is used, the blind area will increase, which is not conducive to event point analysis. To solve this problem, the principle of two-sided filter is introduced, and the two-sided filter is introduced to filter the test data of OTDR. The experimental results show that the two-sided filter can improve the performance of OTDR products while increasing the dynamic range.