The invention discloses a photovoltaic module shutdown device and method and a photovoltaic system, the device comprising a module shutdown device, a group string shutdown device and an alternating current air switch; the group shutdown device comprises a main switch connected with the photovoltaic module, a low-voltage module, a detection module and a first control module; the group string shutdown device comprises a resistance module. The invention judges whether the alternating current air switch is open or not by the magnitude of the main circuit current, thereby controlling the opening ofthe main switch in the module shutdown device; when the main switch of the module shutdown is turned off, the module shutdown device outputs low voltage power through the low voltage module. and through the resistor blocks in the group string shutdown device, low voltage power is converted to low voltage current; depending on the change in low voltage current, the invention judges whether the group string shutdown device is normally connected with the inverter. When the group string shutdown device is normally connected with the inverter, the main switch is controlled to be closed. The invention does not need to control the main switch to start in a short time, so that there is no extra voltage on the DC cable, so as to ensure that the voltage on the DC cable meets the requirements of thesafety gauge standard and improve the reliability.