We conduct a study on 3D seismic b values in southwest Taiwan and provide new insight into the characteristics of seismogenic structures through the heterogeneity of stress distribution and the variations in stress states in a seismic cycle. Our results indicate that, prior to the 2010 Jiasian earthquake and the 2016 Meinong earthquake, significantly low seismic b values occurred in the upper crust. For depths greater than 14 km, stress heterogeneity was more significant. We also propose a new scenario with a block rotation model derived from GPS data to explain how the rupture directions of the 2010 Jiasian and 2016 Meinong earthquakes are associated with the development of new fault systems in the mid-crust region.