Conventional laboratory methods for phosphorus (P) analysis are time-consuming and laborious, which limited the application of rapid P monitoring in water body. In this study, silicon crystal 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 typical wavenumber range of 1200-800 cm–1.