The embodiment of the invention provides a voltage stability preventive control method and device. The method comprises the following steps that: fault stability margin is calculated for each fault in an expected fault set of a power system; faults of which the fault stability margin is smaller than 1 are added into an instability fault set; the sensitivity of a system control vector for the fault stability margin is calculated for each fault in the instability fault set of the power system; a participation control set is selected according to the sensitivity, wherein the participation control set includes variables to be controlled; the sensitivity is substituted into a formula of voltage stability preventive control of the power system, and the formula is solved, and the system control vector is obtained; and voltage stability preventive control is performed on the variables to be controlled in the participation control set according to the system control vector. With the voltage stability preventive control method and device of the invention adopted, technical problems of large computation amount and a large number of control variables caused by incapability of predicting optimal load shedding sites can be avoided, and a plurality of instability faults can be processed simultaneously.