The present invention relates to a time synchronization method in a wireless sensor network. In the present invention, if an upper node requests a lower reference node to start time synchronization, the lower reference node broadcasts a first sync reference packet. The upper node receives the first sync reference packet and transmits the first sync reference packet reception time to the lower reference node. The lower reference node broadcasts the first sync reference packet reception time, such that the other nodes perform time synchronization on the basis of the first sync reference packet reception time. Meanwhile, the lower reference node estimates the first sync reference packet reception time of the upper node to calculate the reception estimation time, and transmits the reception estimation time to a determination node that is two hops anterior to the lower reference node. Therefore, the determination node compares the reception time received from the upper node and the reception estimation time received from the lower reference node and determines whether a capture attack on the upper node has occurred.