The invention provides a method for determining weak nodes in voltage stability based on a matrix perturbation theory. The method is characterized by comprising the following steps: constructing Jacobian matrix conditional number based on the matrix perturbation theory; constructing indexes of the weak nodes in the voltage stability based on sensitivity of the Jacobian matrix conditional number; and establishing load margin indexes of the nodes. The method provided by the invention has the advantages that the matrix perturbation theory is applied to voltage stability analysis of a power system, which opens a new approach for research and analysis of the voltage stability of the power system, overcomes defects of the traditional determination mode of the weak nodes in the static voltage stability and the defects of repeated power flow calculation in a continuation power flow (CPF) method for calculating load margin; and the calculation procedure is simple, the calculation speed is highand the engineering application value is high.