Taking HX,D,3G locomotive as an example, the composition and characteristics of locomotive network system were introduced. The locomotive adopted SHDSL communication technology, and the network data was transmitted through the Ethernet expander (DSL) and common double-core shielded cable. The function of 15 Mbit/s inline communication at 650 meters (18 vehicles)distance was realized. The feasibility of carrier communication technology to realize long-distance and high-speed transmission through DSL was verified. By testing and analyzing the stability of data transmission of locomotive under various control modes such as traction and braking, the optimal configuration scheme of parameters of each component of the system was determined to meet the control requirements of different operation conditions under the vehicle push-pull marshalling mode.