The paper uses the results of focal mechanisms of small earthquakes,seismic apparent stresses,and GPS measuring results to study the variation characteristics of stress field in the Taiyuan Basin before and after the Wenchuan earthquake. The results show that the Wenchuan earthquake greatly affects the tectonic stress of Taiyuan Basin,not only in the direction of stress field but also in the stress value. The tectonic stress field of Taiyuan Basin is mainly the tension stress in NNE-SSW direction before the Wenchuan earthquake,and the compression stress in NEE-SWW direction after the Wenchuan earthquake which is close to the stress field of North China. The change is beneficial to the accumulation of local strain energy and it can be an inducing factor of the active moderate and small earthquake in the Taiyuan Basin.