Disclosed are a photovoltaic shutdown circuit and a photovoltaic system. The photovoltaic shutdown circuit comprises a shutdown power line, a signal receiving module, a signal processing module, and a controllable switch module. The signal processing module comprises a signal modulation unit and a threshold comparison unit. A switch end of the controllable switch module is connected in series to the shutdown power line. The signal receiving module is connected to the shutdown power line for receiving a first signal with a controlling signal; the signal modulation unit is for reverting the controlling signal; the threshold comparison unit is connected to the signal modulation unit to receive the reverted controlling signal and compare the reverted controlling signal with a set threshold to output a driving signal. The controllable switch module is connected to the threshold comparison unit to receive the driving signal and control an on/off of the controllable switch module.