The invention discloses a big data dimension reduction method and device for fault line selection of a distribution network. The method includes the steps of first obtaining big data of fault line selection of a distribution network, and extracting fault characteristic variables; then analyzing the correlation degree between the extracted fault characteristic variables and a line fault result, andcalculating an MIC value between each fault characteristic variable and the line fault result; and comparing the MIC value between each fault characteristic variable and the line fault result with aset MIC threshold value, and screening the fault characteristic variable. According to the invention, the big data dimension when the big data method is used for fault line selection of the distribution network is reduced, and the difficulty of processing big data is greatly reduced.