Abstract: A new mechanism of Higgins-Rijke heat-driven sound is expounded based upon sound energy flux in present paper. Due to temperature gradient of heat source, the phase angle between pressure and particle velocity in standing wave field within Higgins-Rijke tube deviates from 90° and therefore there is sound energy flux in the tube. If the difference of sound intensity between outing from and entering into heat source is positive, this heat source is a sound source; and contrarily the heat source is a sound absorber. The present mechanism can explain not only the importance of heat source location but also almost all phenomena in Higgins-Rijke tubes.