Abstract: The study on temporal and spatial crustal stress change is important for exploring earthquake origin and seismogenic condition. Based on 740 focal mechanism solutions of MLge;2.5 earthquakes occurred during Jan. 1998 to Jan. 2009 in middle Xiaojiang fault and its adjacent area, the studied region was divided into sub-regions, and temporally further divided into phases with the larger earthquakes as boundary of the sub-regions. After removal of the larger earthquakes this paper inverted the focal mechanism data with the method of Gephart for the stress in main phase of each sub-region. The result indicates that the azimuth of maximum principal stress sigma;1 in 4 temporal phases of the sub-region A is approximately NNW-SSE, and in northern part of sub-region B are approximately NNW-SSE，NNW-SSE and NNW-SSE. The azimuth of sigma;1 in southern part of sub-region B is approximately NNW-SSE. The azimuth of sigma;1 in northern part of sub-region B changed significantly, while the azimuth of sigma;1 in sub-region A is relatively stable. This result may be related to the complicated structure and possible stress adjusting in northern sub-region B.The sigma;1 directions in sub-region A may indicate seismically relative stability of the central Yunnan crustal block.