The variable-included-angle plane grating monochromator is broadly used in high performance soft X-ray due to its superior performance, such as high throughput and high resolution. With the development of Science, improving and optimizing the resolution of variables-included-angle plane grating monochromator is necessary and urgently. In order to study and explore the ultra-high resolution of variables-included-angle plane grating monochromator in synchrotron radiation, some issues were researched in this work. Firstly, the relationship between working modes of variables-included-angle plane grating monochromator with different
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ffis emphatically researched. According to the relationship, the high resolution working modes of the monochromator can be selected. Secondly, we studied the effects of high heat load on the optical system by using the simulation software and designed an appropriate cooling system in the optical elements to decrease the effect of heat load on monochromator. The results indicated that the slope error of plane mirror declined from 8.1 μrad to 3 μrad. Lastly, we studied the testing methods of the variables-included-angle grating monochromator with the resolution of already reaching 5×10
4. And the measuring accuracy of angel is 0.026".Those studies will provide some help for designing the monochromator with ultra-high resolution in the third generation synchrotron radiation.