To facilitate loop closing operation，the steady-state and transient process of the loop current are analyzed based on the relevant parameters of power apparatus.It is concluded that after the time delay of over-current protection，the transient current is in general attenuated to a very little value.The transient process of loop current only affects the instantaneous current protection.It is pointed out that the closing loop operation is allowed as long as the summation of the currents through the two feeders to be looped is smaller than the rated current of the feeder.As for the other cases，a simplified criterion without power follow up calculation to determine whether closing loop operation can be safely committed to is deduced.Some examples are given to show the feasibility of the proposed methodology with simulation and experimental results.