The present invention provides a measurement method of length of a distribution network line. The method employs a length measurement device (11) of an electric power distribution network lead, a roller is rolled on a distribution network lead (12) under the action of the gravity so as to measure the length of the lead; and the obtained length of the lead through measured is corrected to obtain the physical length of the distribution network lead. The correction comprises the correction of lead measurement length when the heights of tower rods (13) at two ends of the lead are the same and the correction of the lead measurement length when the heights of the tower rods at the two ends of the lead are different. The method for direct measurement and correction is direct and convenient to measure and small in error, and can obtain very accurate length values; after the length values are obtained, the lead sag and the lead stress parameters can be obtained through calculated, the length and the sag of the leads in different conditions can be obtained according to the temperature and the wind speed so as to evaluate the lead anti-fault capacity, and the lead operation state can be determined through the length of the lead. The measurement method of length of the distribution network line is suitable for the power distribution network and also suitable for lead measurement of higher voltage grades.