Barrier coverage is one of the most important issues in underwater wireless sensor networks (UWSNs). In the past works, the shortest path algorithm is often employed to construct the barrier coverage. However, the computational complexity of the shortest path algorithm (Dijkstra) is high. What's more, the number of nodes constructing barrier coverage adopting Dijkstra algorithm is not small. In this paper, the adjacency matrix-based algorithm is proposed to construct the barrier coverage. In essence, the abscissa of all the randomly deployed sensors imposes certain regularities on searching the adjacency matrix's upper triangle (UT-adjacency matrix), by which we can detect the sensors sequentially to construct the barrier coverage. The following experimental studies demonstrate the effectiveness of the proposed algorithm.