A method of determining priority rules for periodic CSI reporting in carrier aggregation is proposed. A UE obtains channel state information (CSI) feedback for multiple downlink component carriers (CCs) in a multi-carrier wireless communication network. Each downlink CC is associated with a feedback mode, and each feedback mode comprises a set of feedback types to be reported to a base station at time slots configured by an upper layer. The UE then determines a prioritized downlink CC for CSI reporting based on priority levels of the feedback types to be transmitted for each downlink CC at a given time slot. The UE then transmits the corresponding CSI feedback for the prioritized downlink CC at the given time slot via a feedback channel over a primary uplink CC. In one embodiment, different feedback types are prioritized by groups, and each group has several feedback types sharing the same priority.