A specific designed steady-state fiber spectrometer system was applied to measure the optical parameters in rat brain tissue. The reduced scattering coefficient spectrum was obtained from the responding empirical formula, while the absorption coefficient spectrum can be fitted by a unique diffusion theoretical model in near infrared range (650-850 nm). 12 rats were performed in vivo in real time measurements. The range of absorption coefficient in gray matter and white matter of rat brain tissue were obtained from the systemic statistic analysis by applying the empirical formula and theoretical model, and the results were evaluated by tissue phantom experiment. These data have great value in research and clinic applications.