The present application discloses a multi-channel grid-connected power generation system and a control method therefor, which lowers the system cost while reducing no-load losses of all step-up transformers. Multi-channel energy conversion devices in the system are each connected in parallel, by means of a step-up transformer, to the same collector line, one end of the collector line is connected to the grid by means of a switch device, and the on-off switching of the switch device is controlled by a control unit. The control unit sends a switch-off command to the switch device when same has determined that all of the energy conversion devices have entered a non-operating state. In the off state of the switch device, at least one energy conversion device, when meeting a start-up condition, starts to operate as a voltage source, and establishes an alternating-current voltage, so that the phase difference and amplitude difference of voltages at two ends of the switch device are both stable within an allowable error range. Then, the control unit sends a switch-on command to the switch device, and the other energy conversion devices start to operate as a current source to transfer energy to the grid.