A broadband communication network architecture shared by a train control network and a train serving network which has high data transmission security level, wherein the network architecture comprises a trusted network and an untrusted network, said broadband communication network architecture being characterized in that: the trusted network comprises a trusted carriage-level network element provided in each of a plurality of carriages including a front carriage and a last carriage, and a trusted train-level network element provided in each of the front carriage and the last carriage, wherein each of said trusted carriage-level network elements communicates with one of said trusted train-level network elements, and data transmitted in the trusted network comprises control data, monitored data and diagnostic information data of the train control network, and passenger information data and video information data of the train serving network; the untrusted network comprises untrusted train-level network elements respectively provided in the front carriage and the last carriage; wherein the untrusted network is responsible for a communication between the train and a ground; the trusted train-level network element in the front carriage communicates with the untrusted train-level network element in the front carriage via a main security gateway, and the trusted train-level network element in the last carriage communicates with the untrusted train-level network element in the last carriage via an auxiliary security gateway (4, 42), so that the main security gateway (4,41) and the auxiliary security gateway are redundant to each other, wherein when a data communication is performed between the trusted network and the untrusted network via a security gateway (4,41,42) said data to be transmitted between said trusted network and said untrusted network is communicated bi-directionally between the respective trusted train-level network element and the respective untrusted train-level network element, via the corresponding security gateway (4, 41,42). the trusted network comprises a trusted carriage-level network element provided in each of a plurality of carriages including a front carriage and a last carriage, and a trusted train-level network element provided in each of the front carriage and the last carriage, wherein each of said trusted carriage-level network elements communicates with one of said trusted train-level network elements, and data transmitted in the trusted network comprises control data, monitored data and diagnostic information data of the train control network, and passenger information data and video information data of the train serving network; the untrusted network comprises untrusted train-level network elements respectively provided in the front carriage and the last carriage; wherein the untrusted network is responsible for a communication between the train and a ground; the trusted train-level network element in the front carriage communicates with the untrusted train-level network element in the front carriage via a main security gateway, and the trusted train-level network element in the last carriage communicates with the untrusted train-level network element in the last carriage via an auxiliary security gateway (4, 42), so that the main security gateway (4,41) and the auxiliary security gateway are redundant to each other, wherein when a data communication is performed between the trusted network and the untrusted network via a security gateway (4,41,42) said data to be transmitted between said trusted network and said untrusted network is communicated bi-directionally between the respective trusted train-level network element and the respective untrusted train-level network element, via the corresponding security gateway (4, 41,42).