The invention provides a protection method applicable for an extra-high voltage series compensated line with high compensation degree. The protection method comprises the steps of: partitioning the extra-high voltage series compensated line with high compensation degree, and then judging a fault region based on measuring impedance. The protection method solves the problems of possible action rejection of an impedance relay caused by positive short-circuit fault passing through a series compensation capacitor, possible malfunction of the impedance relay caused by opposite short-circuit fault, shortened protection range or exceeding protection, and the like. The transient data in a period of time before the conduction of an MOV (Metal Oxide Varistor) is only utilized in the judgment process of the method, so that the influence from the nonlinearity of the MOV is avoided, correct action of the line protection, correct locking of fault protection of adjacent lines can be realized better, and relatively high reliability is achieved.