Short-circuiting in dc lines affects the security and reliability of dc microgrid greatly. A short-circuit current calculation method for low-voltage dc microgrid is proposed in this paper. To solve the calculation of short-circuit current, a line model of bipolar which includes π-type equivalent circuits, solid-state bidirectional switches with snubber circuits and freewheeling branches is adopted. The line current under different short-circuit fault types in dc bus is discussed and the circuit working mechanisms before and after solid-state switches action are analyzed, and then the analytic expressions of the line fault current are derived. Besides, the freewheeling loop of the short-circuit current is also analyzed after the removal of fault. The correctness of the analytic expressions is verified by MATLAB/Simulink simulations.