We present a method for measuring the refractive index of bio-tissues based on spectral domain optical coherence reflectometry (SD-OCR). Common-path method is used to simplify the system structure and improve the measuring speed. It has a strong anti-interference ability. Broadband light (central wavelength 850 nm) is transmitted through the Y-coupler and scattered (reflected) back to the spectrum analyzing system by the specimen through the sample arm and the Y-coupler. The system construction and optimization are then realized by virtual instruments. Fast Fourier transformation (FFT) is employed to analyze signals. This theory is verified by a standard K9 glass sample and the results show that the experimental error is 0.29%. The refractive index of a cucumber superficial slice at 850 nm is measured and the measuring time is less than 1 min.