The invention discloses a large expandable sunshade cover mechanism applied to a spacecraft. The large expandable sunshade cover mechanism applied to the spacecraft mainly comprises a linear expansion drive component and a cascade-type sleeve component, wherein the main body of the linear expansion drive component is a parallelogram mechanism formed by light-weight carbon fiber rods, and has high admission ratio and light weight. A three-stage sleeve component is formed by connecting three layers of cascade sleeves in series, and is driven to fold and unfold by the drive component. The sunshade cover can provide an on-orbit shading effect for a large optical load; light-weight and low-friction designs are utilized on a structure extensively, so that the large expandable sunshade cover mechanism applied to the spacecraft has light weight and high reliability, and is a space expandable mechanism with high application value on the spacecraft.