Abstract: A method for enhancing data transmission efficiency in a data transmission system having a host, a subsystem and a transmission interface, utilized for the host to transmit and receive a data from a memory of the subsystem via the transmission interface includes steps of the host outputting a query command to the subsystem via the transmission interface for querying available memory utilization of the subsystem; the subsystem outputting a return message to the host via the transmission interface for indicating the available memory utilization according to the query command; and controlling data transmission from the host to the subsystem according to the return message.