A method for processing an interphase short circuit,, wherein a plurality of controlled switches (90, 91, 92, 93) are distributed on a three-phase (A, B, C) ineffectively grounded power supply system, and the controlled switches cut off a line according to a current duration; the method characterized in the steps of: when a simple two-phase or three-phase short circuit occurs in a line, following method (a) is performed, comprising: (a) maintaining a fault phase of the line to be conducted and tripping off remaining fault phases, and artificially grounding another fault phase connected to the fault phase; connecting a neutral point or a charged phase of the three-phase ineffectively grounded power supply system other than the fault phase to a ground, so as to form a closed loop with the fault phase and generate a current, setting a current duration for triggering a cut off of controlled switches at downstream of a power source to be smaller than that for triggering a cut-off of controlled switches at upstream of the power source, and when a certain controlled switch reaches a trigger condition and cuts off the line, stopping the other fault phase from being grounded, and stopping the charged phase or the neutral point from being connected to the ground; and when a two-phase or three-phase short circuit accompanied with a ground fault occurs in a line, the method (a) is performed, or following method (b) is performed, comprising: (b) maintaining a fault phase of the line to be conducted and tripping off remaining fault phases; connecting a neutral point or a charged phase of the three-phase ineffectively grounded power supply system other than the fault phase to a ground, so as to form a closed loop with the fault phase and generate a current, setting a current duration for triggering a cut-off of controlled switches at downstream of a power source to be smaller than that for triggering a cut-off of controlled switches at upstream of the power source, and when a certain controlled switch reaches a trigger condition and cuts off the line, stopping the charged phase or the neutral point from being grounded. when a simple two-phase or three-phase short circuit occurs in a line, following method (a) is performed, comprising: (a) maintaining a fault phase of the line to be conducted and tripping off remaining fault phases, and artificially grounding another fault phase connected to the fault phase; connecting a neutral point or a charged phase of the three-phase ineffectively grounded power supply system other than the fault phase to a ground, so as to form a closed loop with the fault phase and generate a current, setting a current duration for triggering a cut off of controlled switches at downstream of a power source to be smaller than that for triggering a cut-off of controlled switches at upstream of the power source, and when a certain controlled switch reaches a trigger condition and cuts off the line, stopping the other fault phase from being grounded, and stopping the charged phase or the neutral point from being connected to the ground; and (a) maintaining a fault phase of the line to be conducted and tripping off remaining fault phases, and artificially grounding another fault phase connected to the fault phase; connecting a neutral point or a charged phase of the three-phase ineffectively grounded power supply system other than the fault phase to a ground, so as to form a closed loop with the fault phase and generate a current, setting a current duration for triggering a cut off of controlled switches at downstream of a power source to be smaller than that for triggering a cut-off of controlled switches at upstream of the power source, and when a certain controlled switch reaches a trigger condition and cuts off the line, stopping the other fault phase from being grounded, and stopping the charged phase or the neutral point from being connected to the ground; and when a two-phase or three-phase short circuit accompanied with a ground fault occurs in a line, the method (a) is performed, or following method (b) is performed, comprising: (b) maintaining a fault phase of the line to be conducted and tripping off remaining fault phases; connecting a neutral point or a charged phase of the three-phase ineffectively grounded power supply system other than the fault phase to a ground, so as to form a closed loop with the fault phase and generate a current, setting a current duration for triggering a cut-off of controlled switches at downstream of a power source to be smaller than that for triggering a cut-off of controlled switches at upstream of the power source, and when a certain controlled switch reaches a trigger condition and cuts off the line, stopping the charged phase or the neutral point from being grounded.