Nowadays, the monocular zoom video microscope is one of the most widely used detection equipment at mainstream position in the electronics industry. The front objective of this kind of microscope is conducive to the development of its magnification. At present, the mainly similar products design out by non-coaxial system, whose optical axis between front objective and objective is uncoaxial, this method with the aid of the front objective in the Stereo microscope. However, the front objective is using coaxial system in monocular zoom microscope actually. So, Tailor-made a front objective of zoom microscope is imperative. At first, we point out this unique design idea form the special imaging relationship between front objective and objective in zoom microscope .And then we choose the position of entrance pupil、numerical aperture and the layout. At last we enumerated examples which zoom the magnification in, and analyze the design methods of the similarities and differences.