The knee osteoarthritis (KOA) is detected noninvasively and in vivo with nea r infrared spectroscopy on the basis of the change of water content in articular cartilage.The principl e based on Lambert-Beer′s law is stated in this paper.6-month rabbits are used and KOA models are obtained with Videman method.The spectra s of normal knees and OA ones at different time are collected and extracted.The ratios o f light intensities of different wavelengths to 828nm are calculated and compared.Spectral informati on of OA knees is analyzed with linear fitting method finally.Slopes of fitting lines of OA knees at different wavelengths are compared.Spectra of source,normal knees and OA knees are p lotted according to the original spectral data.Compared with normal ones,the near infrared abs orption spectra of OA knees increase.The changes are obvious at 983nm and 995nm.It’s feasible to use near infrared spectroscopy to detect KOA noninvasively and in vivo.The result provides theory basis of near infrared spectroscopy for the clinical detection of human KOA in the future.