The embodiment of the present invention provides a switching method and device of the reactive power control mode of grid-connected equipment and a power system and relates to the technical field of power system grid-connected control, and the frequent switching between an over upper/lower limit mode and a normal operation mode is avoided while the reactive power compensation ability of the grid-connected equipment is not out of use when an AC system is abnormal. The method comprises a step of entering into the over upper limit mode when the voltage of a monitoring point is larger than an upper limit threshold voltage, a step of exiting the over upper limit mode when the voltage of the monitoring point is smaller than (upper limit threshold voltage-hysteresis width) and the current output reactive power of the grid-connected equipment satisfies a predetermined condition, a step of entering into the over lower limit mode when the voltage of the monitoring point is smaller than a lower limit threshold voltage, and a step of exiting the over lower limit mode when the voltage of the monitoring point is larger than (lower limit threshold voltage + hysteresis width) and the current output reactive power of the grid-connected equipment satisfies a predetermined condition.