Spatial information can be described as the range information, direction of arrival (DOA) information and scattering information of the targets in radar detection systems. Spatial information theory is a basic theory for information extraction system such as radar systems using Shannon information theory. The recent research progress and main research work are summarized based on the concept of spatial information, the theoretical and closed-form expressions of spatial information, entropy error, radar resolution, and other basic theoretical issues. The concept of spatial information and its system model are introduced to analyze the spatial information. The theoretical derivation of the quantity of spatial information, the concept of entropy error and its relation to mean square error, the new definition of resolution and its relation to traditional resolution are emphatically analyzed. The theoretical problems that need to be solved are pointed out in the paper. Finally, the development trend of spatial information theory is analyzed and prospected.