Optical mirrors are the important components of a space remote sensor. Their rigid body displacement and surface figure errors are the key indexes for evaluating their environment adaptability. A method for extracting the rigid body displacement and surface figure errors of mirrors from the Finite Element Analysis (FEA) result by the Pantran/Nastran software is presented. First, the raw data output from Patran/Nastran are preprocessed to eliminate their error. Then, a coordinate transformation method and a method of normal equations are used to calculate the rigid body displacement. No ill conditioned matrix problems are found in calculation. Finally, a spherical fitting method is used to calculate the surface figure error. The spherical fitting problem is converted to the optimization problem with three variables and the Gauss-Newton method is used to carry out numerical calculation. The experimental result shows that this method is concise, accurate and fast.