Abstract: A mathematical model of the illumination intensity, which is imposed on the point target by the radar beam step steered, is proposed for the hybrid mode SAR system. By the analysis of azimuth compressed echo signal, combining mathematical deduction, the effects of beam pointing on the image quality are proposed, which are including: the steering time of beam pointing causes infinite paired echo; the hybrid factor causes the extension of the main lobe, which results in the decrease of azimuth resolution; the hybrid factor causes the decrease of the side lobe, which increases the effect of paired echo on the image quality; the interaction of the hybrid factor and the steering time of beam pointing causes aberration of echo. These are also demonstrated by the simulation. Finally, the suggestion of establishment of the hybrid mode SAR antenna beam point steering is proposed.