In response to the current problem of difficulty in achieving extremely short total length and low sensitivity in medium wave infrared zoom systems under conditions of large zoom ratio and long focal length, we design a low-sensitivity medium wave infrared zoom optical system with a total length of only 337 mm and no need for folding optical paths, through the rational allocation of aspherical and diffractive surfaces, as well as adopting a low sensitivity design method for independent components. By reducing the aberration of each component, the system tolerance sensitivity is reduced. The system achieves a 30× zoom ratio and continuous zoom with a long focal length of 30-900 mm. The system has advantages such as a large zoom ratio, long focal length zoom, extremely short total length, low sensitivity, and good image quality within the entire focal length range. It has significant application advantages for military applications such as target recognition, tracking, and detection in narrow spaces.