A method for synchronizing PWM control signals of inverters, an inverter, and a power grid system are disclosed, so that PWM control signals of inverters connected to a power grid can be synchronized. A direct current voltage terminal of the inverter is connected to an external power supply, and an alternating current voltage terminal of the inverter is connected to an alternating current point of common coupling of a power grid, and the method includes: obtaining a phase of an alternating current voltage of the power grid (S101); determining a time period during which the phase of the alternating current voltage varies within a preset phase threshold interval; calculating a period of a preset carrier wave based on a preset carrier wave ratio and the time period (S103); and generating a PWM control signal of the inverter based on a PWM modulation signal and a preset carrier wave (S105).