The invention relates to a computing method for an influence of substation reactive power equipment on transformer winding reactive power, and belongs to the technical field of voltage automatic control in an electric power system. The method comprise the steps of on the basis of real-time power flow computing results, solving a linear equation established between a power flow variable and bus voltage change quantity through adoption of quasi-steady-state power flow; computing a bus voltage amplitude change and a voltage phase angle change in a power grid model after the reactive power is imported into a certain bus; computing relationships between a substation transformer winding reactive power change, and the bus voltage amplitude change and the voltage phase angle change through a branch power flow formula; and computing the sensitivity of the influence of the substation reactive power equipment on the transformer winding reactive power. According to the method, the sensitivity of the influence of the substation reactive power equipment on the transformer winding reactive power is provided, therefore, in the substation voltage automatic control process, the transformer winding reactive power is preestimated after the substation reactive power equipment acts, and the reliability of the control strategy of the substation reactive power equipment is ensured.