The invention discloses a method for completely calculating a grounding short-circuit current of a transformation station. The method comprises the steps: solving the maximum short-circuit current Imax of a power grid through employing a compound sequence network method when an asymmetric short-circuit grounding fault happens; determining three types of neutral point grounding modes; modeling all main elements in the power grid through employing an electromagnetic transient program ATP/EMTP, employing all modules to respectively present all main elements to form a combined model, and then calculating power frequency shunt coefficients Ke1 and Ke2 of external sheaths of a lightning conductor or a cable circuit through employing the combined model; and calculating the grounding short-circuit current according to the above results. The beneficial effects of the invention are that the method determines different parameters according to internal and external grounding faults of the transformer station at different neutral point grounding modes, employs the parameters to calculate the corresponding grounding short-circuit current, can obtain relatively accurate short-circuit grounding current, can provide basis for the design of a grounding grid, and can prevent the lag of engineering progress and the waste of engineering investment.