A routing protocol method for Underwater Acoustic Sensor Networks (UASNs) based on layering and source location privacy (SLP) is provided. (1) A proxy area is selected randomly by a source node. (2) A packet is delivered from the source node to the proxy area through a forwarding probability-based multipath routing algorithm, and a layer-based priority is given to candidate neighbor nodes to alleviate a long detour problem. (3) A proxy node in the proxy area is selected randomly. (4) The packet is delivered from the proxy node to a sink node through the forwarding probability-based multipath routing algorithm. (5) Steps (1) to (4) are repeated until the source node is changed or an adversary finds a position of the source node.