Traditional coordinated control strategies for DC microgrid often overlook the dynamic changes in the power output boundaries of energy sources in droop control, which affects the system, and the mode switching control structure is complex, leading to non-smooth transitions. To address this issue, this paper proposed a unified grid-connected and off-grid coordinated control strategy for a solar-hydrogen-storage DC microgrid. First, a dynamic adaptive droop control strategy was proposed, which utilized the least squares method for data fitting to dynamically adjust the current boundaries, achieving adaptive regulation of the droop coefficient and power source operating state, thereby simplifying the traditional mode switching process and control structure. Second, in combination with practical engineering, an improved grid-connected and off-grid switching control strategy was proposed, which integrated pre-synchronization and outer-loop switching control, effectively reducing impact oscillations during the switching process. Finally, the adaptive droop control and improved smooth switching control were integrated into the proposed coordinated control strategy, and simulations of multi-source, multi-condition mode switching were conducted. The simulation results verified the effectiveness of the proposed coordinated control strategy.