The invention provides a control method and a control device for preventing overvoltage of equipment, and relates to the technical of power transmission and distribution. The control method and the control device can solve a problem of equipment overvoltage caused by an abnormally low DC voltage measurement value and prevent the equipment from being damaged due to overvoltage. The control method comprises the steps of judging whether a measurement value of DC voltage of a rectification side converter station is abnormally low or not relative to an actual value in real time, and if so, switching a DC control system; and judging whether a measurement value of DC voltage of the rectification side converter station is abnormally low or not relative to the actual value after switching the DC control system, and if so, adjusting a DC voltage loop parameter of the rectification side converter station. The control method provided by the invention is applied to a flexible DC transmission system based on a voltage source converter.