The invention relates to a method for reducing line loss by regulating running voltage of a distribution network. The method comprises the following steps: acquiring percentage of fixed loss in total losses, percentage of variable loss in the total losses and rated voltage of a distribution transformer in the distribution network; calculating the running voltage of the distribution network; increasing the running voltage of the distribution network to a voltage minimum value meeting electric power quality when the running voltage of the distribution network is less than the voltage minimum value meeting the electric power quality; and reducing the running voltage of the distribution network to a voltage maximum value meeting the electric power quality when the running voltage of the distribution network is more than the voltage maximum value meeting the electric power quality. The method can regulate the running voltage of the distribution network in real time in the running process of the distribution network so as to ensure that the running voltage of the distribution network constantly runs under the best voltage of the distribution network, thereby reducing the line loss of the distribution network, realizing economic operation of the distribution network, and improving economic benefit of power supply enterprises.