The invention relates to a medium wave infrared continuous zooming optical system with high zoom ratio, belongs to the technical field of optic lens, and aims to solve the existent problems of long zooming stroke, large F value and more lens in the prior art. The system comprises a front fixing group, a lens A of a time changing group, a lens C of a compensation group, a lens B of the time changing group, a lens D of the compensation group, a back fixing group, a secondary image formation group and a probe, coaxially arranged from left to right in sequence, wherein the continuous zooming of the system is realized through the axial movement of the time changing group and the compensation group. Through adopting the structure that the lens A and the lens B of the time changing group and the lens C and the lens D of the compensation group are arranged in a crossing manner to move, the continuous zooming is realized, the zooming stroke is short, the curve is smooth, 100% cold light stop efficiency is satisfied, the F value is constant to be 2, the continuous zooming can be carried out within the range of 10 mm to 300 mm of focal distance, and the image formation quality is sound in the whole focal distance range.