Due to the influence of processing, installation and adjustment of nasal endoscopes in China, the resolution and aberration of endoscopes in actual use are significantly worse than the design level. Through tolerance analysis, it is concluded that the eccentric tolerance has a great impact on the results. Based on the above problems, the installation and adjustment error on the basis of a nasal sinus objective are simulated with a field angle of view of 80 ° and an entrance pupil diameter of 0.2mm, It is proposed that a phase plate is added in front of the protective glass of the objective lens to compensate for the decline of imaging quality caused by the assembly and adjustment error without changing the mechanical structure of the post assembly and adjustment nasal sinus objective lens; It can be seen from the design results that after adding the phase plate, the system transmission diagram increases from 30LP/mm equal to 0 to 170LP/mm greater than 0.2; Using N3 discrimination plate to detect the system resolution, about 18 groups of objects can be distinguished, and the object resolution is 15μm. It can be seen that the design based on the compensation phase plate can significantly improve the image quality without changing the original design.