Operating microscope is a necessary tool in microscope surgical operation, and the object lens is one important part of the operating microscope. The working distance and magnification in the operation should be adjusted to meet the needs of different users, thus a continuous zoom object lens was designed. The continuous zoom object lens is consisted of a set of double agglutinate positive lenses and negative lenses, which is zoomed by mechanical compensatation and moves axially. The operating area of the continuous zoom object lens is from Φ20 mm to Φ125 mm, the working distance is from 150 mm to 350 mm, and the focus is from 230 mm to 400 mm. The interval between the positive and negative lenses and the curve of zoom position was also put forward.