Conventional methods for phosphorus (P) analysis are time-consuming and laborious, which limited the application of rapid P monitoring in water. In this study, silicon (Si) was applied to construct the systems of Fourier-transform mid-infrared attenuated total reflectance spectroscopy (FTIR-ATR) and was firstly applied in P determination in water using the typical P-O vibration with the wavenumber range of 1200–800 cm^–1. FTIR-ATR spectra were obtained using Si crystal (Si-ATR) and conventional ZnSe crystal (ZnSe-ATR).