Abstract: This paper introduces a coal mine runaway car protection system based on PLC technology. The system uses multiple CPU masters, the decentralized control of a single set of car door electric control box, centralized management of the whole car door system; based on the communication scheme between the CPU of Ethernet, data exchange method is presented to solve the problem that other various sets of car door electric control box can not work after the master fault. The system realizes the independent operation and unified management and control of each control station of the runaway car protection system, achieves the goal of system safety and stability, precision and reliability, and reduces the local production halts of the system failure.