In this paper, a new 2-D spectrum focusing algorithm for hybrid spaceborne-airborne bistatic SAR based on space and time domain expansion is proposed. In order to obtain 2-D spectrum, the most of frequency domain algorithm is based on expanding the range history in time domain, but this method can’t represent the spatial characters of scatterer directly; on the other hand, the expansion of range history in space domain doesn’t good to get 2-D spectrum by the principle of stationary phase (PSP). Comparing with traditional algorithm, the algorithm proposed in this paper integrates methods of space and time domain expansion. This mixed-method has advantages that will both represent the spatial character of scatterer directly and get 2-D spectrum by PSP conveniently. It is very beneficial to theoretical analysis and spatial character study of bistatic SAR which has spatial variant characteristic. The validity of algorithm is confirmed through the simulated results.