The objective of this paper is to investigate the connotation, necessity and tendency of Synthetic Aperture Radar (SAR) imaging technology within the framework of multidimensional space joint-observation, which are polarimetry space, frequency space, angle space and time space, on the basis of the key evolvement phases of SAR imaging technology. Furthermore，the definition of Multidimensional Space Joint-observation SAR (MSJosSAR) is given based on the demand of information fusion of multidimensional space joint observation SAR images. After that, the advantage of MSJosSAR is revealed by using Kronecker product decomposition technology for better understanding of target scattering mechanisms. Besides, the hypothesis and basic framework on which the MSJosSAR signal processing rely is listed and illustrated. Finally, the number of joint observation spaces of typical SAR configurations is enumerated.