The invention discloses an improved train control system secure data interaction method, which comprises the following steps of: expanding the shared key of a data transceiver and the length of a random number generated and shared by the transceiver, and calculating a session key with an increased key length by matching with a corresponding SM4 algorithm; dividing the security data X of the train control system into blocks according to N bits, using a data block and a full text of a session key as input in each round, performing iterative computation by using a corresponding SM4 algorithm, and generating an N-bit operation result Hi corresponding to the corresponding data block; regarding the operation result Hi as encrypted data of the corresponding data block, and covering the corresponding data block, so that the security encryption of the security data X of the train control system is realized; and selecting a corresponding lossless compression algorithm according to the type of the train control system security data, performing data lossless compression on the full-text encrypted train control system security data X, and sending the compressed data X to a receiver. According to the method, the data security is greatly improved, and meanwhile, the occupancy rate of wireless resources is reduced.