A novel voltage stability assessment method considering load uncertainty is proposed. It is well known that bus load and total system load are uncertain， commonly only an interval range of load fluctuation can be assured. Firstly， a voltage stability assessment model is constructed. Then， a boundary fixing method is used to find out the worst set of load distributions， which is the closest to the collapse point within the fluctuation range of bus load and total load. The proposed method shed a new light on the voltage stability assessment of a power system with the load uncertainty. Finally， the computational speed and effectiveness of the proposed method is validated on IEEE 14-bus and IEEE 57-bus systems.