In order to improve the output power of 1342 nm distributed feedback (DFB) semiconductor laser, three kinds of cavity surface film combinations are designed in this paper. Electron beam evaporation coating technology is used to coat the cavity surface of the laser, and the output power of the laser under three kinds of film combinations is tested. The results show that the highest output power of 1342 nm DFB semiconductor laser is obtained by using the combination of cavity surface film system (antireflective film: Sub/Al2O3/Ta2O5/Air, high reflection film: Sub/(Al2O3/Si)3Al2O3/Air). The reflectance of the anterior cavity surface is 02%, and that of the posterior cavity surface is 986%. At 260 mA DC, the average output power reaches more than 85 mW (an increase of 856%), and the slope efficiency increases by 829%. The output power of the laser can be greatly improved by coating the cavity surface of the laser with this combination of film systems.