The invention relates to a power distribution line optimization method and system based on multi-dimensional index superposition. Feature quantities of different types of power distribution network lines are equivalently analyzed based on a pre-established power distribution network virtual line case library; structure parameters and technical indexes of the virtual line are determined according to the characteristic quantity; a virtual line in the case library is simulated based on the structure parameters of the virtual line; a correlation degree matrix of the technical indexes is calculatedby adopting an entropy method; a power distribution network transformation project combination decision optimization model of the standard virtual line is established by taking index comprehensive optimization and minimum investment as targets on the basis of the correlation degree matrix of the technical indexes; an optimal solution of a power distribution line transformation scheme is determined by solving the power distribution network transformation project combination decision optimization model; and the operation index of the power distribution network is furthest improved.