The invention discloses a mutual inductance type real-time on-line diagnosis and repair system for the reliability of a long-distance multi-node train line and a use method thereof. The system comprise a host and a slave, wherein an electrical grinding part is arranged on the host and is connected to detected line pairs; a grinding current absorbing part and a slave end voltage detecting part arearranged on the slave and are respectively connected to the detected line pairs; and the grinding current absorbing part is connected with the electrical grinding part through a trigger control wire.Compared with the prior art, the invention has the benefits that: firstly, the real-time on-line detection and the real-time on-line grinding for the reliability of the long-distance multi-node trainline are achieved, the phenomenon that the usability of the line is influenced due to high-frequency detection and line interrupting operation can be avoided, the overhaul and the detaching for maintenance for the parts of the equipment can be avoided, the repair efficiency and the reliability are greatly improved and the loss rate and the cost expenditure are reduced; and secondly, the system has a simple and contact integral structure and is convenient and easy to operate.