Embodiments of the present invention disclose methods and apparatuses for dynamically triggering an uplink sounding reference signal for a carrier aggregation system, methods and apparatus for transmitting an uplink sounding reference signal for a carrier aggregation system. One embodiment discloses a method for dynamically configuring an uplink sounding reference signal for a carrier aggregation system, wherein an uplink schedule in the system comprises an SRS request field. The method comprises: pre-assigning mapping relationships between different values of the SRS request in the uplink schedule and joint coding of a carrier aggregation parameter and at least one user-specific RSR parameters, the carrier aggregation parameter indicating one or more carrier components; determining the carrier aggregation parameter and the at least one user-specific SRS parameter; assigning values to the SRS request field in the uplink schedule based on the pre-assigned mapping relationships, the determined carrier aggregation parameter and the at least one user-specific SRS parameter; transmitting the uplink schedule.