A method of two-stage sidelink control information (SCI) for sidelink transmission is described. In one novel aspect, the SCI is transmitted from a transmission UE (Tx UE) to a reception UE (Rx UE) in two stages. In one embodiment, the 1st-stage SCI carries information related to channel sensing, and is transmitted over a physical sidelink control channel (PSCCH). The 2nd-stage SCI is transmitted over a physical sidelink shared channel (PSSCH) associated with the PSCCH. In one embodiment, the first-stage SCI includes priority information or information of time-frequency resources for the SL transmission. In another embodiment, the first-stage SCI indicates time-frequency location of the second-stage SCI.