The invention relates to a method for dynamically assessing current-carrying capability of high-voltage single-core cables under the emergency load and belongs to the technical field of electrical variable measurement. The method comprises steps as follows: 1) constructing a transient thermal circuit model of the high-voltage single-core cables on the basis of the fundamental principle of the heat transfer theory; 2) determining a step current temperature rise expression of the transient thermal circuit model and variable values in the step current temperature rise expression through the transient thermal circuit model; 3) calculating the time for rise of the cable temperature to 90 DEG C to assess the current bearing capacity of the high-voltage single-core cables under the emergency load. According to the method, on the basis of the temperature rise law change of the high-voltage single-core cables, according to inner dimension parameters and material physical properties of different high-voltage single-core cables, the temperature rise expression of step current is established, the support time of the high-voltage single-core cables under the emergency load is assessed, and the reference is provided for power dispatching.