The invention discloses an equivalent three-phase short circuit calculation method which considers an outer network ground branch circuit and sensitivity information. Firstly, whole-network basic data including system element parameters, a topology structure and a trend calculation result under a normal running condition is input, then based on a sensitivity consistency equivalent method, an equivalent network is constructed, through a sensitivity weighing method, ground branch circuit admittance parameters are deducted, and according to trend, sensitivity and power transfer characteristic consistency, other parameters are solved. Finally, an improved equivalent method is applied to three-phase short circuit calculation, through the adoption of a node impedance method and a superposition theorem and based on the trend calculation result, a short circuit point current under a three-phase short circuit fault of an inner network, all node short circuit voltages and all branch circuit short circuit currents are calculated.