Quantitative knowledge of the film thickness and mass fraction of the urea–water solution is very crucial in many practical applications. Film thickness or mass fraction can only be determined individually by conventional measurement techniques. We develop a novel measurement method to measure the film thickness and mass fraction of urea–water solution simultaneously. The absorption coefficients of urea–water solution (5–50 wt%) are measured, a pair of optimized wavelengths is then chosen to achieve high measurement sensitivity. Cross validation is also performed and uncertainties of the technique are smaller than 0.68% for thickness measurements and 1.86% for mass fractions.