An embodiment of the present invention provides a method for a first UE to transmit a physical sidelink shared channel (PSSCH) in a wireless communication system, the PSSCH transmission method comprising: a step of excluding subframes, used by a second UE, from candidate subframes for PSSCH transmission; and a step of selecting a subframe for transmitting a PSSCH and transmitting the PSSCH, after excluding the subframes, used by the second UE, from the candidate subframes, wherein the subframes used by the second UE include subframes assumed to be repeatedly used by the second UE according to a reservation period of the second UE, wherein, if the reservation period of the second UE is smaller in value than a predetermined value, the shorter the reservation period of the second UE becomes, the greater the number of the subframes assumed to be repeatedly used becomes.