Abstract: High efficiency image reconstruction and inversion algorithm is one of the key technologies for synthetic aperture radiometer. An improved method using subdivision of viewport is proposed for image reconstruction and inversion, in which the viewport is fractionized to a number of sub-viewport of rectangle areas in the algorithm, and the brightness temperature of sub-viewport is retrieved with method of Fourier transform relation between brightness temperature and Visibility Function. The theoretical proof and simulation analysis show that the effects of unavoidable system errors on image reconstruction and inversion are minimized by this method. Comparing with the BG algorithm indicates the validity and effectiveness of the new algorithm, and the computing speed is faster.