The invention belongs to the technical field of a power system and automation thereof, in particular relates to a cross-sectional power transmission capability improvement method considering short-term circuit overload. The improvement method is characterized that the thermal stability of a circuit is verified on the conditions of a known load curve and circuit overload and comprises the following steps of determining an initial value, dividing a stage t0-t1 before overload into n intervals, and calculating a conductor temperature T1 at the t1 moment according to a thermal balance formula; dividing the unequal time frame of an overload stage t1-t2 into m intervals; taking the T1 as an initial value and calculating the conductor temperature T1j at the t1j moment according to the thermal balance formula, wherein j is 1, 2 until (m-1); taking Tmax as the maximum allowable temperature of the circuit, allowing j to be equal to (j+1) and judging whether j is less than m or not when T1j is less than Tmax; judging that the thermal stability of the circuit is satisfied if j is less than m; continuously taking T<1(j-1)> as the initial value and calculating the conductor temperature T1j at the t1j moment according to the thermal balance equation for judgment; judging that the thermal stability of the circuit is not satisfied if j is not less than m; and judging that the thermal stability of the circuit is not satisfied if T1j is more than or equal to Tmax. On the premise of ensuring system safety, the potential power transmission capability of the circuit is developed by means of a traditional power transmission device, and the improvement method has theoretical and practical values.