The invention relates to a direct-current microgrid grid-connected and off-grid handoff bus voltage control smoothing method and system. When a direct-current microgrid is in grid-connected operation, a DC/AC converter stabilizes direct-current bus voltage at a constant value in a constant-direct-current voltage control mode; when the direct-current microgrid operates in an off-network mode or is switched between grid-connected operation and off-network operation, an energy storage converter DC/DC always control bus voltage in a deviation control, so that the direct-current bus voltage is stabilized in a fixed voltage interval, and voltage smoothness and stability in the direct-current bus voltage control mode handoff process is automatically achieved. According to the method, communication between the converters is not needed, background participation and scheduling are not needed, and the autonomous and smooth handoff control over the direct-current bus voltage in the grid-connected operation and off-network operation handoff process of the direct-current microgrid can be well achieved by modifying parameters and strategies of the converters. The smooth handoff control method is easy to implement, simple and reliable.