The theory of power system carbon emission flow has brought new research directions to low carbon electricity field. Accurate calculation of carbon emission flow distribution in power systems according to power flow distribution has become a problem to be solved. Based on the theoretical framework for carbon emission flow in power systems， the similarities and differences between carbon emission flow calculation and power flow calculation are identified. Then influencing factors， calculation systems and steps for carbon emission flow calculation are analyzed and some important matrices and vectors are defined in order to meet the demand of this calculation. Based on the methods of power flow analysis and advanced electric power network analysis， a fundamental method for power system carbon emission flow is established with network losses neglected. Taking IEEE 14-bus system as an example system， the validity of this method is proven.