The invention provides a reliability evaluation method for a physical information system of a back-to-back convertor station based on IEC61850. The method comprises the following steps of (1) obtaining physical equipment sub system information and network information sub system information of the back-to-back convertor station; (2) building an interface matrix of a physical equipment sub system and a network information sub system of the back-to-back convertor station so as to describe the connection relationship between basic elements of the physical equipment sub system and basic elements of the network information sub system; (3) through fault hypothesis, analyzing a network topology structure of the interface matrix; and analyzing the sub fault event occurring probability under the condition of fault hypothesis so as to determine each parameter in the interface matrix; and (4) performing reliability evaluation on the back-to-back convertor station metering the transformer substation physical information system by using the interface matrix. By considering the influence of ICT faults on an electric power system, the electric power system reliability modeling and analysis range is expanded; and the communication network elements are considered, so that the reliability evaluation result is more similar to the practical result.