The invention discloses an ultrasonic detection based unmanned aerial vehicle for search and rescue. The structure of the unmanned aerial vehicle includes an upper rack, dynamic propellers, micro-driving motors, counterbalancing devices, a lower rack, a right support frame, a high definition camera, an ultrasonic emitter, an ultrasonic transducer, and a left support frame. The upper rack is horizontally fixed above the lower rack, and the upper rack and the lower rack are welded together, the four micro-driving motors are vertically fixed at four corners above the upper rack, and are in mechanical connection with a small motor inside the upper rack, and U-shaped grooves of the dynamic propellers are inserted to rotation shafts at the tops of the micro-driving motors. The counterbalancing devices disposed in the unmanned aerial vehicle can timely balance the whole equipment when some spiral power device breaks down, so that the equipment can be fixed stably, thus providing people appropriate adjustment and response time, and preventing the unmanned aerial vehicle from falling.