Abstract: Shenzhen Superconducting Soft X-Ray Free Electron Laser （S³FEL） project plans to adopt dual injector design, and each injector requires one injector cryomodule. Because the superconducting cavity inside the injector cryomodule is planned to be arranged in the structural form of ABBA, the external structure of the cryostat and the internal cooling structure of the injector cryomodule are different from that of the standard cryomodule. The design of cryostat for injector cryomodule is introduced in detail. The strength, deformation and temperature field distribution of key components are analyzed by finite element method. The position change of superconducting cavity is evaluated at low temperature, which provides a theoretical basis for the design of cryostat for injector cryomodule.