By changing the network， the new ports are constructed and a unified method is given to simulate loop-opening and short circuit faults. At the new port boundary， the faulted weakly meshed network is divided into two networks， i.e. the pure radial symmetrical network and the unsymmetrical network to simulate loop-opening and short circuit faults. Then the short circuit current and the compensation current calculation formulas are obtained. According to the relationship among branch current， nodal injection current and nodal voltage， the branch current and nodal voltage calculation method is given. A new method to calculate weakly meshed distribution network short circuit faults is presented. It has the following characteristics:（Ⅰ） a unified and simple loop-opening and short circuit fault simulation method capable of simulating any kinds of faults easily including double-point-to-earth fault;（Ⅱ） a highly efficient fault calculation algorithm based on the branch impedance parameters instead of node impedance parameters;（Ⅲ） adaptive to network topology change;（Ⅳ） easy and direct calculation for the faultless branch current and node voltage. Case study results demonstrate that the proposed algorithm has good computational efficiency and accuracy.