The traditional microscope usually needs to change the magnification of the system by changing the magnification of objective lens, which is same as that of the eyepiece, and the magnification is not continuous. Applying the continuous zoom optical system design to the microscopic imaging system can realize the continuous change of imaging magnification. Continuous zoom optical systems and their zoom principles are summarized in this review. Various types of continuous zoom microscopes are discussed. The future development of continuous zoom microscopes are also discussed and prospected.