Most of our domestic infrared detector’s photosensitive surface is less than the pixel surface area. A part of the incident light irradiates to the photosensitive area between the dead zone, and this part is not used but reflected and scattered. The microlens array with specific size was fabricated by photoresist fusion method, then a micro-lens array was used to converge to a 1 μm ~3 μm infrared detector, the surface area of the infrared detector can be expanded to reduce noise of the infrared detector and prevent incident light from entering the dead zone. The main process steps include: substrate cleaning, coating and glue, soft baking, exposure and development, baking, hot melt, ion beam etching and so on. The specific process steps: first, in order to obtain the photoresist pattern re-quired for the micromirror curvature, we chose the AZP4620 positive photoresist for the thick film, and the re-fractive index of the photoresist was 1.64. Second, the substrate treatment, removing the substrate surface grease and other impurities to ensure that the substrate and the photoresist had good adhesion. Third, the substrate was coated with a uniform photoresist, and the photoresist was placed under the mask plate which had been set in ad-vance and subjected to UV exposure, the corresponding cylindrical colloid was formed by the development of the image; Fourth, the substrate put into the rapid annealing furnace for hot-melt, the photoresist was heated in the rapid annealing furnace, the surface area of the melted photoresist would shrink to a minimum and the surface energy was the lowest due to the combined action of the surface tension and the substrate adhesion. After the hot melt getting a stable spherical crown microlens must require photoresist cylinder that reduced the amount of gravity is equal to the increase in the amount of potential energy. In the experiment, not any size and the thickness of the cylindrical colloid can form good spherical surface shape after hot melt to meet the design requirements of spherical shape by the photoresist cylinder diameter size, height, and the infiltration degree of glue and basal de-cision. Photoresist as an amorphous polymer is composed of a variety of chemical composition. The melting point of the photoresist is not an accurate temperature, but a temperature range in which the state of the photore-sist exhibits a liquid state. Because of the different types of photoresist, the melting point range is different. Finally, the uniform microlens array was obtained with an ion beam etch machine. By optimizing the temperature and time parameters of each step process, the microlens with a crown diameter of (5.5 ± 0.5) μm and a radius of cur-vature of 3 μm was realized, the microlens had good uniformity and consistency, and the infrared detection was carried out in the 1 μm ~3 μm band device requirements.