The present invention relates to a method of transmitting buffer status report (BSR) by a node in a wireless communication system. In particular, the method includes the steps of: transmitting, to a parent node, a first BSR with starting a timer before receiving data from a child node; triggering a second BSR based on receiving the data from the child node; and based on the data not being transmitted to the parent node until expiration of the timer, transmitting, to the parent node, a scheduling request (SR) for transmission of the second BSR, wherein, based on the data being transmitted to the parent node before the expiration of the timer, the timer is stopped and the second BSR is canceled.