The invention provides a method and system for determining control parameters of a photovoltaic grid-connected inverter. According to the method and system, firstly, a system small-signal model is established for the photovoltaic grid-connected inverter; then, a root locus diagram of the system small-signal model is drawn; finally, according to the root locus diagram, a group of parameter values capable of enabling main system characteristic values to be away from an imaginary axis are selected as the control parameters. Due to the fact that according to the method and system, the control parameters are directly selected through a root locus method without repeated tests, the problems that repeated tests are needed in an existing method for determining the control parameters, time and labor are saved, and work efficiency is low can be solved.