Abstract: With the continuous development of infrared technology, infrared continuous zoom lenses have been increasingly widely used. As an important component of an infrared continuous zoom lens, the mechanical structure serves to support the optical lenses and related electrical components of the infrared optical system. To ensure the imaging performance and specifications of the infrared optical system, the structural design must take into account the requirements for the relative positional accuracy between lenses, as well as the precision control of lens decentration and tilt. This paper takes a specific infrared continuous zoom optical system as the research object, and on the basis of meeting its optical performance requirements, completes the mechanical structural design of the optical system and proposes a precise alignment method suitable for optical lenses. Detailed alignment procedures are presented, and experiments are conducted to verify the feasibility and effectiveness of the proposed method.