Aimed to the feature for long after work distance of double Gauss long focus optical system,double reflection mirrors was designed to refraction ray, the camera′s size was shortened, with saved space and reduced quality. System′s image had not change by analyzing reflex action matrix calculation after jionting two pieces of reflection mirror. The precision thread trim mechanism was designed for adjusted the pitch and azimuth angle of reflection mirror, then fixed. A image demacrating tool was designed that combing with corss line and radiation shape, and a adjustable observation tool with multiple microscope combination, efficiency was improved. A method combine with coarse and precision was planned out to demarcate focus, finally the image plane calibration was finished. This method has been proven was feasible in the practical work.