Abstract: The grating scanning spectrometer has incident and emergence lights with fixed directions. It works when its grating rotates. It′s different from another lightsplitting system in which the grating is fixed, and the direction of the incident light changes. Based on the equation of the grating, the angular dispersive power, line dispersive power and resolving power of the spectrometer testing system whose grating movement was controlled automatically by a computer were calculated theoretically. The parameter formulae of the angular dispersive power, line dispersive power and resolving power of the grating scanning spectrometers were obtained. The calculated result shows that the measurements made by the grating scanning spectrometers are different from those of the spectrometers with fixed grating.