A rotate-in-group zoom optical system can realize dual/multiple field-of-view (FOV) switch,and according to its characteristics the relation of rotate-in-group lenses focus and system′s lenses spacing,focus,F number and magnification factor is retrieved. Rapid switch is achieved for a rotate-in-group zoom optical system when a narrow FOV subsystem changes to a wide one after a rotate-in motion of two negative-positive separated lens groups. Meanwhile,in the wide field mode,the FOV switch lens group is located outside the active narrow-field ray-bundle without intersection. The derived formula is proved by the design of a focal plane array-based midwave infrared rotate-in-group zoom optical system. The designed system has rapid dual/triplex FOV switch,limited lens number for narrow FOV subsystem,and large operation range,and meets the requirement of infrared search and track.