The mesa-type InSb infrared focal plane array (IRFPA) detector typically has a simple fabrication process and high quantum efficiency. However, its filling factor is low, and it will further decrease with the reduction of the pixel size. Reducing the corrosion depth of the mesa can improve the fill factor of the detector, but it will increase the crosstalk. A novel design and preparation method for microlens arrays is introduced to improve the filling factor of InSb infrared detectors and reduce the crosstalk. Compared with the existing reflow microlens arrays, the filling rate, surface roughness, and size uniformity of this microlens array are well balanced, and it can be directly fabricated on the surface of InSb infrared detectors with a simple process. The results show that the crosstalk of the detector decreases by 26% and the optical response increases by 22%.