The invention discloses a secondary virtual circuit failure locating method based on differential approximate reasoning of a failure area. The secondary virtual circuit failure locating method comprises the following steps: at first, carrying out virtual link and physical link modeling on a process layer network connection of a "net sampling and net hopping " or "point sampling and net hopping" intelligent substation, and carrying out association mapping configuration on a virtual link and a physical link; using a directed graph theory to carry out model abstraction on the process layer network connection of the intelligent substation, and abstracting to obtain a directed connected graph; and then, according to communication link abnormality information sent by a receiving side, when receiving failure of the virtual link, starting a failure diagnosis locating system, judging the on-off state of the virtual link to continuously iterate a difference set of the physical link for loading the connected virtual link and the disconnected virtual link, and locating a physical link failure point position causing the failure of the virtual link. The secondary virtual circuit failure of the intelligent substation is monitored, judged, diagnosed and located to assist an operation and maintenance staff to quickly find the failure, remove the failure and recover the normality, so as to guarantee the safe and reliable operation of a power grid.