The original structure and the added balance layer structure of the 2048×2048 (15 μm) infrared focal plane dewar cold head are analyzed by finite element method. Adding a balance layer with a lower expansion coefficient under the ceramic substrate can relieve the deformation and thermal stress of the detector chip to a certain extent. By increasing the diameter of the upper surface of the AlN balance layer, the warpage range beyond the center of the chip is reduced, and the problem of excessive stress concentration is alleviated. When the diameter exceeds the diagonal length of the chip, the maximum thermal stress decreases sharply, and finally tends to be stable; the deformation of the chip decreases rapidly. When the diameter is 36 mm, it reaches a minimum of 6.86 μm; then it increases slowly and tends to be stable. When the diameter of the AlN balance layer exceeds the diagonal length of the chip, the influence of the thickness of the AlN balance layer on the chip deformation begins to decrease. The deformation and thermal stress of the large area array focal plane detector chip can be effectively improved by adding an AlN balance layer. The reliability of the detector Dewar component can be further optimized by adjusting the structure of the AlN balance layer.