The nighttime OI135.6 nm airglow is proportional to the square of the maximum electronic density of ionospheric F_2 layer (N_mF_2). Based on the previous studies of the nighttime O1135.6nm airglow radiative and emissive model,the retrieval algorithm of N_mF_2 derived from nighttime OI135.6 nm emission was presented. The column emission rate is calculated for each grid point of the nighttime airglow radiative and emissive model. The electron density profile,O~+ density profile, and electron temperature profile are taken from the IRI2000 model, and the neutral components are taken from MSISE90 model. In order to derive the relationship between the OI135.6 nm column emission rate and N_mF_2,the column emission rate is fitted to the square of N_mF_2 linearly. The ratio of the square of N_mF_2 to the column emission rate is obtained from the slop of the fitting line, which gives the relationship between N_mF_2 and the emission. According to the measurements of the OI 135.6 nm column emission rate,N_mF_2 are retrieved. Finally, the error of the retrieval method is analyzed,which provides important theoretical supports for the time and space applicability of the algorithm.
