A new-style system that automatically measures the diffraction efficiency of plane reflection grating was designed.The continuous illuminant was adopted for illumination,the duplex grating spectrograph structure was applied,and the linear array NMOS was the receiving component.Wielding relevant principle of the grating spectrograph,theoretical analysis principle was carried out for the testing system.Integrating the aberration theory of geometrical optics,the image quality of this optics system was analyzed.Analysis indicated that the systematic device structure is compact,and electronics system is simplified.The system does not have the problem about wavelength sweep synchronization of the two grating spectrographs,and its wavelength repeatability is very good.So the precision is easy to guarantee.Compared with the former automated scheme,the production cost is reduced,moreover it is easy to operate,and the working efficiency is enhanced.The study showed that this automatic measurement instrument system features a spectral range of 190-1 100 nm and resolution is less than 3 nm,which entirely satisfies the design request.It is an economical and feasible plan.