Two-dimensional layered materials represented by MoS2 and GeS exhibit excellent physical properties in optical and electrical aspects. How to combine the excellent properties of the two materials and obtain composite materials with new synergistic functions are of great significance to the development and application of electronic devices. This work uses the first-principles calculation method of density functional theory to systematically study the electronic structures and optical properties of GeS/MoS2 heterojunctions, at the same time, the influence of interface distance, strain and electric field on the electronic structures and the optical properties of the heterojunctions was also explored. The research results show that the GeS/MoS2 heterojunctions is a type Ⅱ band arrangement, which is conducive to the separation of photogenerated electron-hole pairs. Further research found that the band arrangement and light absorption coefficient of GeS/MoS2 heterojunctions can be effectively controlled by means of strain and electric field. The research results show that GeS/MoS2 heterojunctions has potential applications in photocatalysis, optoelectronic devices and other fields, and the research in this paper provides theoretical guidance for the design and preparation of GeS/MoS2 related optoelectronic devices.