The invention discloses a method for controlling deformation of a metal feed waveguide in a space environment. The method comprises the following steps of S1, determining geometric structure parameters and material attributes of the metal feed waveguide according to a satellite-borne passive planar reflective array antenna; S2, determining a structure of an elastic bracket according to a structure layout, boundary conditions and performance requirements of the metal feed waveguide; S3, building a finite element model of the metal feed waveguide according to the geometric structure parameters and the material attributes of the metal feed waveguide; S4, calculating thermal stress distribution and a thermal deformation value of the metal feed waveguide in the space environment according to constraint conditions and a thermal load environment of the metal feed waveguide; and S5, determining an elastic force range of the elastic bracket according to the thermal stress distribution and the thermal deformation value, thereby finishing deformation control of the metal feed waveguide in the space environment. According to the method, the elastic bracket is designed, so that the difficulty in heat resistance design of the metal feed waveguide is overcome and the deformation control design of the metal feed waveguide in the space environment and an emission stage can be guided.