The embodiment of the invention provides a method for remotely modifying a definite value, a master station, a stability control device and a system. The method comprises the steps of sending a modification instruction for modifying a target definite value to a target device to enable the target device to modify the target definite value according to the modification instruction, and recording the modified target definite value into a definite value editing area; receiving telemetry data and definite value data sent by the target device, wherein the telemetry data include a detection value obtained through detecting the target definite value and the definite value data include the modified value of the target definite value stored in the definite value editing area; according to the telemetry data and the definite value data, judging whether the modification operation is successfully done or not. According to the embodiment of the invention for remotely modifying the definite value, the remote operation safety and the remote operation reliability for unattended substations in the power grid can be improved.