The present disclosure disclosed a method of determining a buffer status report (BSR). The method comprises obtaining, by a user equipment (UE) from a buffer, data item to be sent; determining, by the UE, a size of the data item to be sent; determining, by the UE, a minimum number of required logical channel groups (LCGs) based on the data item to be sent; and determining, by the UE, at least one BSR with flexible length based on the size of the data item to be sent and the minimum number of the required LCGs. Information of the at least one BSR with flexible length includes the minimum number of the required LCGs, LCG identifiers (LCG IDs) respectively associated with the minimum number of the required LCGs, and at least one buffer area corresponding to the LCG IDs.