Grating scatter is an important performance index for plane grating ,and its measurement is a difficult problem for grating research field .In order to achieve stray-light of the instrument itself to be less than 10-8 so that the grating scatter can be accurately measured ,stray light in diffraction grating monochromators has been studied and an opto-mechanical model of meas-ure instrument for plane grating is designed ,which works in parallel light environment and based on the scalar diffraction theory and classical Fresnel-Kirchhoff diffraction theory .Main pathway of the instrumentation’s stray light is calculated and analyzed by the simulation of stray-light testing equipment with ASAP software .Accordingly ,four stray-light suppression structures in-cluding blocking rings ,vanes ,aperture stops and light traps are proposed to reduce instrument’s scattered light and grating’s multiple diffraction .Finally ,contrast analysis of the instrumentation’s stray light is made before and after adding stray-light suppression structures .Simulation and analysis results show that the max of instrument’s stray light reduces from more than 10-6 to less than 10-8 after adding stray-light suppression structures and has met the stray-light testing equipment’s design re-quirements whose goal is to realize accurate measurement greater than or equal to 10-7 for grating scatter with grating’s groove density changing from 300 to 3 600 gr · mm -1 .The research methods and results above will provide a theoretical basis for the research and development of the stray-light testing equipment for plane grating .%杂散光是平面光栅的重要性能指标，光栅杂散光的测量一直是光栅研制领域的难题。为实现仪器自身杂光低于10-8量级，以满足对平面光栅杂散光10-7量级的精确测量要求，基于标量衍射理论和经典Fresnel-Kirchhoff衍射理论，对光谱仪器中的光栅杂散光进行了理论分析，设计了平行光照射条件下光栅杂散光测试仪的光机模型。利用杂散光分析软件ASAP建立紫外单色光入射下光栅杂散光测试仪的散射模型并对其进行仿真计算，分析仪器杂光的主要来源及散射路径，据此提出了用于降低仪器散射光和光栅多次衍射光的挡光环、叶片、光阑、光学陷阱等四种杂光抑制结构。最后，采用ASAP软件对增加抑制结构前后的仪器杂光相对强度进行了对照分析。仿真及分析结果表明，仪器杂光在测试波长±100 nm范围内的最大值由采用杂光抑制结构前的10-6量级以上降低至10-8量级以下，已满足光栅杂散光测试仪的设计需求，即可实现刻线密度为300～3600 gr · mm-1的光栅杂散光10-7量级精确测量。该研究方法及结果将为平面光栅杂散光测试仪研制提供理论依据。
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