A bridging module, a data transmission system, and a data transmission method are provided. The bridging module obtains a first read request, and allocates a first data storage space for first return data corresponding to the first read request. The bridging module combines a first master transaction identifier and an address of the first data storage space as a first slave transaction identifier of the first read request, and sends the first read request to a slave device. The bridging module obtains a second read request, and allocates a second data storage space for second return data corresponding to the second read request. The bridging module combines a second master transaction identifier and an address of the second data storage space as a second slave transaction identifier of the second read request, and sends the second read request to the slave device.