The method involves moving AUV to an observation point according to preset speed and depth. A detection sensor is started to perform observation process of an ocean element profile by using an automatic driving unit. Judgment is made to check whether preset observation time is reached. Posture of AUV is leveled and adjusted by immersing in a buoyancy control device to a depth of rest. A supervision duty control unit is entered into a supervision state. Judgment is made to check whether wakeup process is triggered. AUV dormancy is monitored when wakeup process is not triggered. Wake-up process is performed by using a supervisor duty control unit according to different wake-up reason.