The aim was to develop a nonlinearity model of quantitative analysis of vitamin C content by infrared spectroscopy and provide theoretical basis for nondestructive testing of vitamin C content in drugs. The infrared spectrum of vitamin C was smoothed and noise-eliminated by wavelet transform, which may obtained smooth curve and enhanced spectrum resolution. Absorption peak about 3000cm-1 was selected as characteristic absorption peak to set up linearity or nonlinearity model. The result showed that nonlinearity model, correlation coefficient 0.9967, had more nicety than that of linearity model. The result of traditional titration of iodine as reference system, relative deviation of nonlinearity model was 2.75%, but that of linearity model was 28.03%. It was feasible and effective to determine vitamin C content by infrared spectroscopy based on nonlinear modeling.