The invention discloses a distribution network loop closing power supply switching method. The method comprises the following steps: proving that a linear relation exists between bus load on two sides of a loop closing point interconnection switch and loop current complex power of a loop closing point through analysis; deriving a practical calculation formula of a steady-state current and an impact current of an interconnection line outlet circuit breaker through simulation; introducing the practical calculation formula into an SCADA system; calculating the steady-state current and the impact current of the interconnection line outlet circuit breaker, and calculating the sum of load currents of two interconnection lines; then comparing with related data, and judging whether the operations of loop closing, loop disconnecting and power supply switching can be performed accordingly. The method disclosed by the invention is simple and practical, data are easily acquired, and equipment does not need to be added, so that complicated complex operation is avoided, the method is easy to implement, higher in precision and accuracy and lower in error, a powerful basis can be provided for the distribution network loop closing power supply switching operation of a power dispatcher, the power distribution reliability is effectively improved, the outage cost is reduced, and the method has extremely high application values.