Optical filter is widely used in multi-spectrum imaging of space remote sensor. Usually the base of the filter is optical glass. And optical coating on the glass is used to filter the specific spectrum. Plane wave transmitted wavefront testing is the main technique used to evaluate the wavefront distortion of the filter. The wavelength of the light interferometer uses is fixed. It can not cover the filter’s spectrum. And it is impossible to test every spectrum transmitted wavefront of the filter. In order to solve this problem, one solution was provided in this article. The interferometer with one fixed light wavelength was used. The front and back surface sag data, transmitted wavefront data of the filter before coating, and the front and back surface sag data after coating were used in a special algorithm together, the plane wave transmitted wavefront of the filter after coating can be obtained. The theoretical derivation of the algorithm was fully discussed in this article. And the experiments show the error of the transmitted wavefront RMS can be less than 0.004λ (λ=632.8 nm). The technique can be applied on the testing of infrared filter, experiments show the error is about 0.002λ (λ=3.39 μm), The accuracy requirement is satisfied and the cost is reduced.