The invention provides an overcurrent protection method and device for a line between/inside a transformer station in a ring network power supply system. The overcurrent protection method includes thefollowing steps: after optical fiber differential protection of the ring network power supply system fails, when an incoming line overcurrent protection device detects that a current of a corresponding line is greater than a corresponding protection current, if a corresponding outgoing line overcurrent protection device detects that the current of the corresponding line is not greater than the corresponding protection current, the incoming line protection device executes an overcurrent protection action; and when the outgoing line overcurrent protection device detects that the current of thecorresponding line is not greater than the corresponding protection current, if the corresponding incoming line overcurrent protection device detects that the current of the corresponding line is greater than the corresponding protection current, the outgoing line protection device executes the overcurrent protection action. According to the technical scheme provided by the method and the device,the judging method is simple, is fast in protection action, is not restricted by protection areas, and can solve the problem that failure is poor when a backup protection system performs incoming lineovercurrent protection on the line between transformer substation in the prior art.