Common method of spectrometer miniaturization is implemented by decreasing the size of optical components and the distance between them, which will reduce the system performance. In order to achieve high throughput, high spectral resolution infrared spectral detection, a design method of a miniature spectrometer based on ZnSe planar waveguide is proposed. First, the principle of beam compression by planar waveguide is described. Then, in accordance with the diffraction properties of grating in ZnSe medium, the relationship between the spectral resolution and the various optical parameters is deduced. Finally, a specific design of a miniature spectrometer is given. The spectral range of this spectrometer is 8~14μm, the spectral resolution is 80 nm, numerical aperture is 0.3. The optical system is a monolithic ZnSe planar waveguide, the size is 70 mm×70 mm×4 mm. A comparison between this spectrometer and common Czerny-Turner of the same design specifications is done. The results show that miniature spectrometer based ZnSe planar waveguide has very small size, good spectral resolution and high throughput.