The invention relates to a fast protection method for preventing overcurrent of a current-limiting resistor in a startup process of a flexible DC transmission system. The protection method comprises afast overcurrent section protection input/exit basis, a fast overcurrent section I/section II/section III protection action criterion, a corresponding fixed value setting method and a protection logic, wherein the fast overcurrent section protection input/exit basis is that the current-limiting resistor is in a working condition and is located in a charging circuit; the fast overcurrent section I/section II/section III protection action criterion is magnitude of charging current and maintenance time requirements; fixed value protection is protecting a fixed action current value and protectinga fixed delay time value; the protection logic is protecting an exit action when the fast overcurrent protection action criterion of any section is met, protecting exit locking when the protection action criterion is not met, making the current-limiting resistor exit the charging circuit and exiting fast overcurrent section protection after charging time is reached. The invention aims at providing the fast protection method for the overcurrent of the current-limiting resistor.