The traditional satellite size estimation method based on RCS data mainly uses ellipsoid model for equivalence, which is not accurate enough for estimating the size of rectangular satellites. This article mainly studies the size estimation technology of rectangular satellite. Based on the RCS equivalent formula of the rectangular flat plate that constitutes the rectangular satellite, the relationship between the length and width of the rectangular flat plate and the RCS sequence characteristics is studied; By modeling the motion attitude of a rectangular satellite, the calculation of the satellite’s in orbit motion attitude angle has been achieved. Based on the above research, a method for estimating the size of rectangular satellite based on RCS data is proposed, which can estimate the length and width of rectangular satellite by using RCS data. The experimental results show that this method can effectively improve the accuracy of size estimation for rectangular satellites, providing a new method and idea for spatial target feature recognition.