An underwater wireless sensor is provided. The underwater wireless sensor comprises a floating-diving device enabling the underwater wireless sensor to dive to a first predetermined water depth in response to a predetermined condition; a sensing device converting a plurality of environmental parameters into a plurality of environmental messages; a micro controller receiving the environmental messages and sending a command signal including the environmental messages; and a communication device receiving the command signal, sending the command signal via a wireless sensor network, receiving an external message including a second predetermined water depth, and sending the external message to the micro controller so that the micro controller performs a corresponding operation and sends out a control signal to enable the underwater wireless sensor to move to the second predetermined water depth.