Return-type large-bore long-working-distance auto-collimating microscopic monitor

The invention discloses a return-type large-bore long-working-distance auto-collimating microscopic monitor and relates to a large-bore long-working-distance auto-collimating microscopic monitor. The return-type large-bore long-working-distance auto-collimating microscopic monitor solves the problems of short measurement distance of an existing microscopic monitor, low microscopic resolution ratio of a monitoring system and narrow monitoring view field. Emergent light of a light source passes through a reticle, a second beam splitter, a second reflecting mirror and a first beam splitter prior to being incident to a to-be-measured target, a light beam reflected by the to-be-measured target returns along an original light path, and transmission light is split from the position of the beam splitter by the return light path and is incident to a collimating CCD (charge coupled device). After being reflected by the to-be-measured target, the beam sequentially passes through a first reflecting mirror and a primary o