Linewidth narrowing module is an important component of excimer laser for lithography. The installation angles of prisms and gratings affect the system output characteristics directly. In order to improve installation and debugging technique of linewidth narrowing module, we study the influence of the angle deviation of the prism in the prism expander on the energy and linewidth of the system. Through the theoretical derivation and experimental verification, we analyze the influence of individual prism angle deflection on the energy and linewidth of the excimer laser system, and determine the alignment error of each prism. The experimental results are in good agreement with the theoretical analysis results. The alignment method for optimizing the linewidth narrowing module design according to the alignment error has guiding significance for the spectrum control engineering.