Abstract: ‍ ‍The improvement of phased array antenna in electronic scanning ability has made the multi-azimuth-angle mode one of the development directions of spaceborne synthetic aperture radar （SAR）， which can interpret the target information from multiple dimensions. However， a strong two-dimensional “fan-shaped” sidelobe phenomenon exists in the publicly available multi-azimuth-angle fusion SAR images with different two-dimensional distribution characteristics， leading to the target misjudgment. Therefore， this paper focuses on the “fan-shaped” sidelobe phenomenon and target resolution. First， the multi-azimuth-angle mode is introduced， and a fast back-projection （BP） algorithm based on CUDA parallel computing is proposed for efficiently generating sequential SAR images. This imaging method can avoid time-consuming image registration and geometric correction. Then， based on the geometry relationship between slant-range plane and ground-range plane of multi-azimuth-angle SAR， the resolution and sidelobe direction along azimuth and range direction on the ground-range plane are analyzed. The analyses reveal the origin of “fan-shaped” sidelobes in fusion SAR images and provides the reasons for the different characteristics of two-dimensional sidelobes. As a result， the geometric relationship between the satellite and the observation scene and the number of fused images are derived. Finally， the effectiveness of the proposed analysis results of the “fan-shaped” sidelobe is verified using point targets and through the extended targets simulation experiment. The experimental results indicate that the accuracy of resolution analysis along both the ground azimuth and range directions is better than 0.02 m and that of the sidelobe direction is better than 1°.