Abstract: The backscattered average ultrasonic power of biotissue is related to its temperature.This theory includes (1) the model of discrete random medium is considered with biotissue. (2) the average backscattered ultrasound power depends on the attenuation and velocity in biotissue. Theoretical analysis indicates:to an aqueous scatterer in a water-based medium(e.g.pig liver), when temperature increased, backscattered average ultrasonic power increased with attenuation while decreased with the ultrasound velocity. Experimental result shows:the average backscattered power is changed with temperature obviously and can be measured. Based on this result, a new noninvasive temperature estimation method is advanced and confirmed here.