The present disclosure discloses a charging system, a lightning protection method for a terminal during charging and a power adapter. The charging system includes a power adapter and a terminal. The power adapter includes a first rectifier, a switch unit, a transformer, a second rectifier, a first charging interface, a second voltage sampling circuit, and a control unit. The control unit adjusts a duty ratio of a control signal such that a third voltage with a third ripple waveform outputted by the second rectifier meets a charging requirement, and controls the switch unit to switch on for a first predetermined time period for discharging when the voltage value sampled is greater than a first predetermined voltage value. The terminal includes a second charging interface and a battery. When the second charging interface is coupled to the first charging interface, the second charging interface applies the third voltage to the battery.