The substorm is a dissipation process of the energy stored in the magnetotail, causing active auroras in the nightside polar regions. What processes in the magnetotail trigger the substorm is a major issue in magnetospheric research and has been extensively debated for decades. To understand the substorm triggering mechanism, I statistically studied substorm-associated evolution of the near-Earth magnetotail, using more than ten years of plasma, and magnetic and electric field data mainly from the Geotail spacecraft. I also analyzed data from the recent five THEMIS spacecraft. My results revealed the overall morphological picture of substorm-associated magnetotail evolution as well as energy release and transport and clarified that magnetic reconnection in the near-Earth magnetotail plays an essential role in substorm triggering.