The invention provides a method and device for judging voltage instability of load substations. The method comprises the steps of firstly calculating power transfer voltage drop coefficients between converter buses of DC systems and high-voltage side buses of the load substations; preliminarily judging voltage stability of the load substations; and finally judging whether voltage stability verification needs to be carried out on the load substations or not by combining the proportions of different loads in the load substations and carrying out simulation through power system simulation software, thereby achieving judging whether voltage instability of the load substations occurs or not according to the simulation results. According to the method and the device, simulation calculation for various faults of all DC systems is not needed, and the load substations with hidden dangers and faults in voltage stability are obtained on the basis of the power transfer voltage drop coefficients and the proportions of different loads in the load substations for targeted verification and simulation, so that guidance is provided for safe and stable operation of a power grid, and the workload of safe and stable verification of an AC-DC hybrid power grid is reduced.