The invention provides a method and system for determining Ward equivalent parameters of a power system. The method comprises the steps of: determining a boundary node admittance matrix according to voltages and current data of boundary nodes of the power system and determining injection currents of the boundary nodes according to the boundary node admittance matrix, wherein the voltage and current data of the boundary nodes of the power system comprise: voltages before and after short-circuiting of the boundary nodes, currents flowing from internal networks to the boundary nodes before and after the short-circuiting of the boundary nodes and earth short-circuit currents of the boundary nodes. According to the technical scheme provided by the invention, the structure of a conventional power system is not needed to be modified; the currents flowing from the internal networks to the boundary nodes before and after the short-circuiting of the boundary nodes are considered; and therefore,the obtained ward equivalent parameters are more accurate, the workload is reduced and the engineering cost is saved.