Beamsplitter coating is one of the optical devices which is based on interference phenomenon. The performance of this coating is separation incident beam into two transmitting beam and reflecting beam in optical system. In this research, design and fabrication of three multi-layer dichroic beamsplitter coating has been studied that can be used to separate 3.5-5 um (in reflectance channel) and 8-12um (in transmittance channel) wavelength regions with a combination of low index materials and high index materials for thermal imager camera. Considering the traarency of selected materials in desired wavelengths, Ge/IR-F625, Ge/BaF 2 and PbTe/IR-F625 were choosen for high and low index materials as first, second and third designs of dichroic beamsplitter, respectively. Design of multilayer structure was performed based on quarter wave stack. Design and optimization of coating structure was performed by the Essential macleod software. Tooling factor of material that used in fabrication of this coatings was measured. The amount of measured tooling factor for single layers of Ge, PbTe, IR-F625 and BaF 2 is 0.93, 0.94,0.95 and 0.96, respectively. Deposition was performed by physical vapor deposition technique in a vacuum chamber by using electron gun and thermal boat. The bonding layer Y 2 O 3 was used to coating stability and increase adhesion of interfaces layers to each other and to the substrate. The IR reflection spectra was measured with Fourier transform infrared spectroscopy. Environmental analysis such as abrasion, adherence, temperature and humidity were performed on the coating. First coating was not approved due to shelling, The second coating was not approved due to lack of favorable traarency and dispersion in the wavelength regions of interest. Against third coating is approved due to favorable traarency and passing environmental tests successfully without change in structure as the final coating in accordance with military and optical standards. The effects of factors such as temperature change and incident angle change were also studied in the coating. Because importance of residual stress in thin film coating, in this research was measured exprimental residual stress with measurment of radius curvature of substrate and semi-exprimental residual stress with macleod software for second and third dichroic beamsplitter. Results indicated that there is a good fitness between the results of these two methods values. For structural analysis, the final multilayer coating was analyzed with field emission Scanning Electron Microscopy cross section, atomic force microscopy and nano indentation and Fourier transform infrared spectroscopy.