The TH-1 satellite is the first stereo mapping transmission satellite in China, and the primary mission goal of the satellite is for topographic mapping at 1:50 000 scale and high-accuracy location without Ground Control Points (GCPs). 1st, 2nd satellites of TH-1 were launched on August 24, 2010, May 6, 2012, and 3rd satellite was launched on October 26, 2015. Now, three satellites of TH-1 are well operating on its orbit. After evaluation, the location accuracy of 1st satellite without GCPs is 10.3 m/5.7 m (horizontal accuracy/vertical elevation accuracy), and the location accuracy of 2nd is equivalent with 1st satellite. In this paper, the system overview of TH-1 and the key technical in ground image processing are introduced. Then, the preliminary location accuracy of 3rd is assessed. The results are shown using three routes images:the location accuracy of 3rd is higher than 2nd, and can realize high accuracy location without GCPs, in which the horizontal accuracy is 7.2 m, and the vertical elevation accuracy is 2.6 m.