Abstract: Objective: To address the issue of reactive power backflow caused by a decrease in system power factor, it is necessary to study the optimization strategy for metro reactive power compensation. The capacity design of SVG (static var generator) in metro traction power supply system under centralized reactive power compensation is emphatically studied. Method: Taking a line of Guangzhou Metro as example, at initial operation stage of the metro line, the load processes during peak and offpeak periods at a THS (traction voltage reduction hybrid substation) are fieldmeasured and analyzed. Based on the urban rail transit DC traction power supply simulation platform and train operation diagram of an actual trajectory, the AC/DC alternating iterative power flow calculation is performed to compare the simulated and fieldmeasured results of THS rectifier unit load process, thus validating the effectiveness of the proposed algorithm. Under the premise of meeting the power factor requirements at the PCC (point of common coupling), a design method of SVG reactive power compensation capacity is proposed. Considering the initial, near and longterm train schedules of the test line comprehensively, power supply simulation is carried out for peak, offpeak, and nonoperating periods, and the required reactive power compensation is calculated. Based on its optimization strategy, the SVG installation capacity is determined. Result & Conclusion: In the case study, the maximum reactive power compensation required for the 35 kV side SVG connected to the left transformer of the main substation MSUB2 is 7.19 MVar, it is 2.81 MVar for the right transformer 35 kV side SVG. Considering a margin of approximately 10%, equipment selection is performed for SVG, and installation capacities for the left and right transformers 35 kV side SVGs are 8 MVar and 3 MVar respectively. This reactive power compensation optimization strategy is applicable for SVG capacity design of metro lines under centralized compensation scheme.