Abstract: The parameters measurement method and operating principle of the conical scanning MWIR optical system were introduced. The adjustment methods of the measurement system were discussed, and the stray light analysis had been done by using the FRED software in allusion to the no ideal imaging. After analysis of the spread spot, the blur was introduced from the stray light of high reflection metal coating on pinhole substrate of infrared collimator. The stray light was restricted effectively by co-centered mica plate close to the substrate. In addition, if the infrared under tested correcting lens coating transmission was not high enough, there would be regular shape stray light at four corner of infrared detector. This kind of influence could be eliminated with image process program. Finally, the accuracy of the parameters measurement system for the conical scanning MWIR optical system was practical tested, and the results showed that the accuracy met the requirement.