Abstract: The magnesium alloy cabin casting is a thin-walled cylindrical component with an inner flange structure. It is easy to deform out of tolerance during heat treatment and subsequent machining, which reduces the qualification rate of the type of component. The deformation mainly comes from the deformation generated during the heat treatment and the deformation caused by the residual stress caused by the heat treatment on the subsequent machining. With a large magnesium alloy module casting, the heat treatment and machining finite element model were established, the deformation rules of cabin casting during heat treatment was analyzed. Meanwhile, the influence of residual stress generated by heat treatment on subsequent machining deformation was studied. The residual stress after heat treatment is taken as the initial residual stress under machining and the influence of different rough processes on the deformation of cabin casting. The results show that the cabin casting is deformed seriously during the heat treatment, and the installation of tooling can better suppress the deformation during the heat treatment of the cabin casting. The rough machining that removes the tooling before the outer circle is conducive to reduce the deformation of the cabin casting.