Abstract: In the study of the observability and controllability of the power grid, in order to obtain the short-circuit capacity of the power grid more timely and accurately, this paper proposes a measurement technique based on the disturbance curve fitting method. By removing a certain capacity of reactive power compensation capacitor on the bus to be tested, causing bus voltage disturbance, obtain the voltage value before and after the disturbance and its phase angle difference θ. Based on the circuit model of the substation and the basic theorem of linear circuits, the short circuit of the bus to be tested is derived calculation formula for capacity. In-depth exploration of the measurement of the important parameter θ（voltage phase angle difference） of the short-circuit capacity of the power grid, reveals that the voltage vector phase change caused by switching capacitors is a key factor affecting the measurement accuracy, and proposes a curve fitting method to measure the angle difference. The Simulink simulation model of short-circuit capacity measurement is built. The simulation results show that the short-circuit capacity measurement technology based on the disturbance curve fitting method solves the problem of on-line short-circuit capacity measurement very well, compared with the traditional off-line calculation method, it is more simple and accurate.