Wall spectral emissivity solution is one of the key techniques for infrared stealth of aircraft. Firstly, the wall reflected light path and light source were designed, and the brightness sequence of wall reflected radiation was obtained by spectral radiometer. In order to eliminate the influence of external interference on the solving accuracy of spectral emissivity as much as possible, Bi-LSTM brightness regression network model was designed based on bidirectional LSTM network, and the test samples were trained and learned. The wall emissivity solution model based on BRDF and the luminance regression model based on Bi-LSTM network were used to solve the wall emissivity. The calculation results show that the relative error of the proposed wall emissivity solution method based on BRDF is 12.21%, which meets the requirements of engineering test.