Abstract: After the watermelon juice was processed by heating, it would produce strong unpleasant smell, which would seriously affect the normal flavor of the watermelon juice. In order to find out the key off-flavor of thermal treatment watermelon juice, the volatile compounds of watermelon were comprehensively extracted by solid phase micro extraction (SPME) and solvent assisted flavor evaporation (SAFE), then they were analyzed by GC-O-MS to do qualitative and quantitative analysis. The overall flavor of thermal treatment watermelon juice was prominent in cooking flavor, whose formation was the result of the combination of various compounds. The six key off-flavor compounds of watermelon juice were preliminary identified, including trans-2-heptenal (soap, bitter almond), trans-2-octenal (fat, coffee), hexanol (flower, bitter), dipropyl disulfide (onion, sulfur), decanal (soap, pungent), n-octanol (metal, burnt), and these six compounds were verified by the construction of recombinant models.