The development of a deep-sea methane sensor that can accurately, in real-time and in-situ, obtain hydrothermal methane data is of great significance for deep-sea research. Previously, two kinds of optical imaging interference systems that use methane radiation spectrum to detect and retrieve methane state parameters have been proposed. Firstly, based on the molecular spectral radiation theory, the theoretical relationship between molecular radiation spectrum and concentration, temperature and pressure is established. Then, combined with the characteristics of a high-pressure deep-sea-environment, the deep-sea molecular radiation model based on the Lorentz spectra line is established. The model provides a theoretical basis for the inversion of state parameters such as molecular concentration, temperature and pressure by spectral legal quantity. At the same time, it provides a powerful tool for deep-sea molecular spectrum simulation. Then, with the help of the molecular basic spectral line parameters provided by the HITRAN molecular spectral database, the light source spectral line of the methane imaging interference system is selected. Comparing the characteristic absorption spectra of CH₄ molecule with CO₂, H₂S, H₂O and other molecules in the 5 990~6 150 cm^-1 band, the intensity of the CH₄ spectral line is about 2~3 orders of magnitude higher than that of interfering molecules, and the six effective spectral lines of methane are evenly distributed in this band, with a spectral line spacing of about 2~3 nm, which is very suitable for temperature and other state parameters detection by the spectral method. Therefore, six methane spectral lines (1 640.37, 1 642.91, 1 645.56, 1 648.23, 1 650.96 and 1 653.72 nm) with weak spectral line interference, uniform spectral line distribution and moderate spectral line spacing are selected as the target light source spectral lines of methane imaging interference detection system. Finally, based on the deep-sea molecular radiation model and the basic spectral line parameters of methane in the HITRAN database, the radiation spectrum data of methane with arbitrary concentration, temperature and pressure are synthesized, and the variation characteristics of methane radiation spectrum with concentration, temperature and pressure are analyzed. For a single central spectral line, the radiance of methane molecules increases linearly with the increase of concentration, increases nonlinearly with the increase of temperature, and decreases nonlinearly with the increase of pressure. For the full band spectral line, the full width of the methane radiation spectrum widens with the increase of concentration and temperature and narrows with the increase of pressure. The theory and simulation results of the deep-sea methane radiation spectrum established in this paper can provide data support and a theoretical basis for developing and data inversion of marine in-situ methane sensors based on the spectral method.