A novel micro infrared spectrometer was designed which is different from traditional grating scanning one. This micro spectrometer introduced an uncooled infrared detector LiTaO3 with high sensitivity and small volume, and a MEMS pulsed infrared light source was adopted as emitter and chopper, which threw off traditional mechanical chopper. Combined with the design of a two-double light route, the volume of micro spectrometer was made even smaller. Primary results show that the design method of micro-infrared spectrometer is feasible, the wavelength range of instrument is wide, from 2000 to 5000 nm, and spectrum bandwidth is about 45 nm, which can be used for the sample analysis, such as plastic films, biologic liquid, environmental gas and so on.