Abstract: The fundamentals of imaging observation in synthetic aperture radiometer were present in this paper. The system parameters in synthetic aperture radiometer, such as brightness temperature sensitivity, integral time, antenna beam width, target brightness temperature, background noise temperature, operate frequency, target equivalent sectional area and so on were analyzed and the relationships between them and system operate distance were derived. The system observation performance was certificated through simulation and the methods for compensating the array errors such as inconsistent were discussed. The research results will be help to promote the engineering implementation of synthetic aperture radiometer.