The traditional tongue inspection method should be urgently improved due to the relative large diagnosis error probability caused by the excessive dependence on the Chinese physician’s experience and judgment. But the application of tongue diagnosis based on image processing is limited by some factors including the performance of light source, image acquisition device and the low recognition rate of similar color for different diseases. In order to overcome these drawbacks, the spectroscopy method was employed to analyze the tongue by using the unique fingerprint effect of tongue spectrum. A spectrometer for tongue diagnosis (STD) was developed to achieve this goal in this paper. Meanwhile, to overcome the shortcomings of traditional light-splitting devices, a plane holographic concave grating was used as the diffractive grating, which not only can improve the luminous flux efficiency and miniaturize system, but also improve the spectral imaging quality and resolution. Experimental results demonstrated that the spectral range of STD reached 340～850 nm, and its spectral resolution is better than 2 nm. And the result of simulation experiment validated the feasibility of spectrometer’s system.