The invention provides a direct current transmission line protection method and system for lightning protection and prevention of an abnormal large number. The method and the system determine the current difference value and the current break variable of a line by collecting a current at the side of a direct current transmission line, determine whether a preset starting protection criterion, a abnormal large number prevention protection criterion by utilizing the difference accumulation amount and a abnormal large number prevention protection criterion by utilizing the current break variable are established or not according to the current difference value and the current break variable of the line, and determine whether the direct current protection action is output or not according to theresult of the criterion. The direct current transmission line protection method and system for lightning protection and prevention of an abnormal large number can prevent the direct current protection action outlet from misoperation under the conditions of lightning stroke and an abnormal large number and ensure high sensitivity of faults in the area.