In view of the actual problems existed in the routine infrared jamming technology, such as failure to meet required energy concentration, poor concealment and unable to be realized zoom, a design scheme regarding a new offaxis double mirror type of laser jamming applied at beam expander was put forward. The opticalmechanical structures of such key components as the battery of offaxis double mirrors, the steering mirror and supporting and fixing mechanisms, etc. were designed and analyzed. A newstyle structural design of offaxis was adopted, realizing zoom function of the expansion ratio; the design of microstress was adopted for components of both the main and secondary mirrors and the components of steering mirror. Analysis results show that the first order natural frequency is 108.3 Hz, and stress responses of the structure is also smaller than yield limit of the material; in the temperature range of －20℃ to +60℃, the maximum displacement of the main and secondary mirrors is below or equal to 0.01mm and the surface accuracy is below to 71.9 nm. After the actual detection, the beam expanding ratio obtained is 1:10.02(19.92, 25.02), meeting the requirement of designed technical index. Analysis and experimental results demonstrate that designs of the optical and mechanical structure are effective that can meet the requirements of actual applications.