To improve the processing ability of asymmetrical eletromechanical side fault as well as the flexibility of electromechanical and electromagnetic transient hybrid simulation,a calculation method of complex asymmetrical fault in the electromechanical and electromagnetic side at the same time is proposed.This method obtains the fault circuit admittance matrix according to the type of asymmetric fault.By modifying the admittance element associated with the faulty node,the fault circuit admittance matrix is superimposed on the normal admittance matrix to obtain the admittance matrix after fault.The network solution is finally achieved by solving the network equation after fault.Based on the linear circuit superposition theorem,the Thevenin equivalent voltage of the interface node is calculated.To reduce the modeling scale of the electromagnetic side,positive sequence equivalent conductance of the interface is used for the conversion of the Thevenin equivalent voltage into Norton equivalent current.At last,through the electromechanical and electromagnetic transient hybrid simulation platform of a IEEE 39 system containing a HVDC line based on PSCAD+C frame,the simulation accuracy and effectiveness of the method is validated.