In allusion to the current practical problem of small duty ratio, low light energy utilization in infrared focal plane array, the manufacture of square aperture spherical microlens array and integrated application with infrared focal plane array are studied. Starting with the character of microlens arrayinfrared focal plane array, the advantages of square aperture spherical microlens array and round aperture spherical microlens array are compared. The laser direct writing varying dose exposure making technology of square aperture spherical microlens array is proposed, and the mathematical model of photoresist exposure and the square aperture spherical microlens array surface figure functions are established, based on which the direct writing varying dose exposure software is written. Related process experiments are carried out by the model number of laser direct system and plasma etching machine from Changchun University of Science and Technology. The infrared quartz spherical microlens array is made, of which micro-lens element size is 40×40 μm2, spherical radius is 60 μm and element spacing is 1 μm, and then is integrated with the square aperture spherical microlens array with infrared photosensitive array. The results show that the duty ratio achieves 95%, and the utilization ratio of light energy increases from original 60% to 90%. It can be concluded that the way using square aperture spherical microlens array instead of the round aperture spherical microlens array can significantly improve sensitivity, signal-to-noise ratio and resolution ratio of the infrared detector.