Abstract: Power integrity (PI) problem is essential when analyzing high speed signal passing through power ground. The fundamental mode in power ground is the zero-order parallel plate mode, which is capable for 2D simplification. However, in areas around anti-pads and other z-axis discontinuities, 3D algorithm has to be adopted to improve the accuracy. A hybrid 2D/3D discontinuous Galerkin time domain (DGTD) method has advantage on both accuracy and efficiency, thus is effective to cope with such full wave simulations. The 2D and 3D domains share the same triangular prism mesh. With appropriated basis functions, different domains can couple with each other efficiently. As the electromagnetic wave propagates, the 2D/3D domain decomposition is dependent both on space and time. This work proposes an improved adaptive criterion which monitors the field at every time step, thus updates the 2D/3D domain dynamically. Unlike the state-of-the-art technique controlling absolute error, the proposed criterion controls comparative error. This method is both high efficient and accurate, and flexible for various kinds of structures. Some numerical examples are demonstrated to validate the proposed method. Comparisons with commercial software are also given.