Fouling prediction method, and membrane filtration system

A fouling prediction method in a membrane filtration system for filtering raw water containing ions and salt components, the method involving a step for irradiating raw water before being filtered by the membrane module with excitation light of a plurality of different wavelengths, a step for measuring the fluorescence intensity of fluorescent light generated by irradiating excitation light of a plurality of different wavelengths, and a step for predicting the occurrence of fouling by using a coefficient set for each wavelength range of the fluorescent light and the value of the measured plurality of fluorescence intensities.