The analysis of the complexity of electric vehicle （EV） users′ charging demand and action law is the fundamental work to improve the robustness and resilience of distribution network in the context of large-scale EV integration. Existing researches made little efforts on the description of the derivative nature of EV charging demand. Firstly, starting from the origin of charging demand, a transportation power coupling network model is established based on the spatiotemporal trajectory of EV user activity travel to reveal the medium mechanism of EV in the transportation power coupling system. Secondly, from the perspective of transportation, an activity travel chain model is established considering the characteristics of EV user activities and travel behavior, and EV charging demand is predicted based on the Logit model. A logit-based model is applied to predict EV charging demand. Then, from the perspective of the power grid, an evaluation system for the impact of EV grid connection is constructed based on indicators such as voltage offset severity, maximum power transmission margin of the line, and power system line losses. Finally, based on simulation, the influence of EV charging loads in different regions on the power grid under different scenarios is analyzed with the coupling degree of transportation and electricity as the regulating variable, providing theoretical support for guiding EV users to schedule and manage orderly charging in the temporal and spatial dimensions.