Extreme ultraviolet lithography (EUVL) is recognized as a leading technology in next-generation lithography. Achieving spectral purification while ensuring extreme ultraviolet (EUV) reflectance is one of the key technologies for industrializing EUVL. An EUV collector mirror with phase grating can be used in the spectral purification of an EUVL source. However, it also induces a considerable loss of EUV. We propose a deposition model for calculating the multilayer coating profile on the surface of an EUV collector with grating based on a geometric line tracing method. In addition, it also analyzes the coating defects that influence the EUV reflectance, and the evolution of the coating defects with the grating positions. Experimental results reveal that the model accurately predicts the multilayer coating profile deposited on the surface of the collector, which helps improve how EUV collector is deposited.