This paper analyzes the traditional X-ray fluorescence method to measure the zinc layer thickness of galvanized sheets layer. It proposes a measuring method of galvanized zinc layer based on total reflection X-ray fluorescence analysis technology, and the X-ray total reflection model is set up for simulation in the MCNP. When the X-ray total reflection occurs, zinc layer will almost make the X-ray source reflect completely, associated with a small amount of X-ray fluorescence producing in the normal direction of the galvanized sheet. Using this X-ray fluorescence to analyze directly can effectively reduce the scattering background of source X-ray, improve the accuracy of measurement and reduce the required source X-ray energy. The Simulation results demonstrate that the feasibility of the X-ray total reflection on galvanized sheet, it provides the theoretical basis for practical application.