Spatial resolution is the main characteristic of imaging system. It depends on various factors such as pixel area and pixel aperture, system noise, signal and background illumination levels, spectral range, and system MTF. To determine the resolution for given levels of signal and background illumination and spectral density of radiation, at first, it is necessary to calculate the number of photons which are transferred through multilayer coating of the imager and photogenerate carries giving a contribution into signal current or charge packet. Then full system noise consisting of input, photogeneration, thermogeneration, scanning, and output noises is determined. After that the system MTF including consideration nonlinear effects may be calculated and system resolution is determined. The resolution may be calculated for given wavelength or spectral range of input radiation. The main equations, algorithms for modeling and some results of simulation are described.