The invention discloses an electric transmission line longitudinal protection method based on a parallel reactor. The invention builds an inside fault model and an outside fault model of an electric transmission line based on a fault component network, the inside fault model and the outside fault model are changed and simplified into a uniform induction model, an inside fault and an outside fault are judged according to the size and the symbol of XL through identifying the inductance XL in the fault models, thereby solving the problems that a traditional differential protection is easy to cause faulty action when suffering from the outside fault and is not sensitive enough when suffering from a high-resistant grounding fault, greatly improving the relay protection property, and passing the simulation validation.