Sagnac spatially-modulated interference imaging spectrometer and Offner convex diffraction grating imaging spectrometer are focused on,and their signal- to- noise performance is seriously analyzed.Through derivation of the spectral radiance of their acquired image pixels under same observation condition,it is shown that spatially-modulated interference imaging spectrometer no longer has high throughput and multiplex advantages so that its signal-to-noise is lower than diffraction grating imaging spectrometer.Further,the latter’s signal-tonoise ratio advantage becomes more significant as the increase of spectral band number.