In order to realize the fast and high accuracy alignment of Coude optical system，a pentaprism alignment method based on the principle of self-collimation is presented. The principle and assembly method of Coude optical system are given. By errors analysis in the Coude optical system,the result shows that the errors of Coude optical system aligned is within 15″,which meets accuracy requirements of Coude optical system. This method can be used in the Coude optical system,and also has reference value for the installation of reflective mirrors.