In order to meet professional requirements for the portable and high-performance Raman spectrometer, a small near-infrared (NIR) Raman spectrometer for biomedical detection was built in this work. In addition, assembly system was completed through the theoretical calculation, geometric optical path design. Differences from the traditional structure with reflective collimation were shown as below. (1) Transmission-based collimation method was adopted in dispersion system of the spectrometer, so the collimated scattering light projected onto the grating for dispersion. (2) Following dichroic mirror for reflection and penetration, objective lens converging the incident light and collecting the scattered light, the Raman spectrometer was designed to meet confocal plane at the slit between the collection unit and dispersion system, which is useful to collect the Raman signal and remove the stray light. (3) The spectrometer system achieves the high-resolution (3 cm-1), high repeatability and high sensitivity for spectral detection ranging of 500~2 200 cm-1 (785 excitation). (4) The entire optical system was designed in the size of ca. 240 mm×200 mm×130 mm, therefore achieving miniaturization for this NIR Raman spectrometer and flexible assembly of components. It was then used to measure Raman spectra of glucose and knee cartilage and get excellent results by comparing with that obtained by huge commercial Raman spectrometer. The results show that the spectrometer has high resolution, high reproducibility and high sensitivity, etc, thus it can be flexibly applied in biomedical and other research fields.