BPA short-circuit current calculation software is widely used in China, however, with the same source data its calculation result differs under different calculation conditions or with different methods and thus affects power grid planning and decision-making. With consideration of current calculation standards for short-circuit current, different assumptions for node operating voltage in different calculation methods are analyzed, the diferences of line charging power and load model construction with different calculation modes are analyzed, and the resulting differences of short circuit impedance and current calculation are discussed. Using improved New England 39 bus system and Sichuan power grid planning architecture in 2020 as examples, short-circuit current calculation results under different calculation conditions and with different methods based on BPA are compared to verify the variation of the theoretical analysis. Finally, some suggestions for the choice of short-circuit current standards are made.