Infrared optical system is vital for aircraft in the terminal stage. As a fragile part of optical system, optical windows are under the threat of external environment, which could bring interference and damage to the windows. With the development of laser theory and technology, laser protection becomes more and more important for infrared optical windows. Laser protection can be sorted as linear protection, nonlinear protection, phase transition protection and so on. Among those protection methods, linear protection has the characteristic of low-cost and high performance on small angles incident, which is suitable for optical windows in the terminal stage. Linear protection method usually includes multilayers which have high reflectivity during the wave band of laser. Due to the small scale, high reflective films have lower laser damage endurance. Thus the laser induced damage theory of thin film is widely discussed around world. The relevant study about high laser induced damage threshold thin film is usually on single layer and double layers, also the film material is in visible band. It’s important to know the laser damage of laser protective multilayer for infrared optical window. Therefore, the laser thermal effect and optical characteristic of a laser protective/mid infrared anti-reflective multilayer is studied. A model of laser damage on laser protective/mid infrared anti-reflective multilayer is establish (Fig.1) with the help of finite element analysis method. Using two couples of material HfO₂/SiO₂ and ZnS/YbF₃, two types of multilayers are designed on ZnS optical window substrate. By comparing the optical performance and laser thermal effect(Fig.3-Fig.4), the multilayer structure of HfO₂/SiO₂ is used for further study. Single variable method is chosen and the effect of thickness, reflective index and extinction coefficient of layer material on multilayer is studied. By comparing infrared window without protection, infrared window with single layer coating and infrared window with laser protective/mid infrared anti-reflective multilayer coating, the result shows that laser protective/mid infrared antireflective multilayer can reduce the temperature of optical window when laser incident. The analysis of HfO₂/SiO₂ multilayer concludes three parts: thickness of top three layers, reflective index of HfO₂ and SiO₂, extinction coefficient of HfO₂ and SiO₂. All three variables can influence the temperature of multilayer, reflectance at 1.06 μm and average transmittance during 3-5 μm. When the error of thickness of top three layers goes to 10% larger than the ideal value, temperature of multilayer grows to 88% higher, reflectance at 1.06 μm becomes 0.5% lower and average transmittance during 3-5 μm becomes 0.2% lower. When the error of reflective index of HfO₂ goes to 10% smaller than the ideal value, temperature of multilayer grows to 55% higher, reflectance at 1.06 μm becomes 14.4% lower and average transmittance during 3-5 μm becomes 1.7% lower. The result shows that film/substrate temperature grows one order of magnitude higher when extinction coefficient k_L grows two orders of magnitude higher. When the extinction coefficient of SiO₂ grows 1×10^-5 larger, the temperature becomes 93 degrees larger, meanwhile the temperature becomes 25 degrees larger for HfO₂ at the same condition. When preparing optical multilayers, there always have error on structure and material properties. By establishing finite element analysis model about laser protective/mid infrared anti-reflective multilayer on ZnS substrate, thickness, reflective index and extinction coefficient are studied to confirm the relationship with multilayer laser thermal effect and optical properties. At the range of -3%-3%, influence of thickness and reflective index error on temperature and optical properties can be ignored. By comparing two materials, the change of temperature caused by extinction coefficient of SiO₂ is much stronger than HfO₂, which mean that reducing the extinction coefficient of SiO₂ is a good way to reduce laser thermal effect and advance the ability to endure laser attack. The study can provide an idea for designing laser protective and mid infrared antireflective multilayer with high induced laser damage threshold.