The invention discloses a new energy distribution network backup protection time limit optimal design method and device. fault line quick search based on cut current is performed on a distribution network; optimal design is provided for new energy distribution network backup protection time limit according to the results of fault line quick search. The cut current principle and the DG (distributedgeneration) treatment manner are adopted, a protection control center is utilized to design a fault line quick search scheme for a new energy distribution network with DG; the protection control center provides optimal design for backup protection time limit for fault lines and adjacent superior lines; a cut current fault search principle and new energy distribution network backup protection timelimit optimization scheme is designed; current protection criteria of all lines in a search area are not modified; only setting time for in-situ protection for the fault lines and adjacent superior lines is optimized; regular time that is fixed is maintained for the protection for other lines; in-situ protection is subject to the original time setting before receipt of a wide area issued command.