The design of a double-band infrared detector stacked structure microlens array was introduced, which was modeled from the angle of actual light and optimized by using the principle of optical non-imaging theory, taking into account the requirement of microlens processing linewidth. According to the diffraction efficiency of the microlens, the calculation method of the factors affecting duty cycle was analyzed and explained in detail. The design method was novel and unique, which was based on the actual incident light. The method was verified to be feasible by coupling the processed microlens with the detector. Some inspiration is given to the designer of microlens arrays, which can be used in the design of microlens arrays for other multi-layer detectors.