The invention provides a turn-on control method of a turn-off device. Each turn-off device receives a turn-on instruction in batches or a bus capacitor is pre-charged before each turn-off device receives the turn-on instruction, or each turn-off device receives the turn-on instruction in batches again after the bus capacitor is pre-charged, so that a condition that all components provide continuous large current starting to charge from zero to the bus capacitor at the same time through the turn-off device can be avoided, and the problem in the prior art that the service life of the bus capacitor is influenced through the continuous large current is solved. The invention further provides a photovoltaic system; the problem in the prior art that the service life of the bus capacitor is influenced through the continuous large current is solved through technical characteristics.