This paper was aimed to study the aqueous two phase extraction (ATPE) on water soluble bio oil(SBO), in which ethanol, K2HPO4, NaH2PO4 and (NH4)2SO4 were selected to form the water soluble bio oil(SBO) aqueous two phase system (ATPS). After phase separation, the extraction rates and the volume ratios of the upper to lower layer of the ATPSs were investigeted. Both the upper and lower layers of these SBO ATPSs were analyzed by elemental analyzer and Fourier transformation infrared spectrometer (FTIR). The different extraction rates indicates the influnces of different salt during the phase saperation, of which NaH2PO4 has less effect to SBO than the other two; K2HPO4 may neutralize some organic acid; the lowest extraction rate of ethanol/(NH4)2SO4 system indicates the effects of (NH4)2SO4 to SBO. Too much ethanol will fech in more water, hence the optimizational ratio of the SBO ATPS should be SBO:salt:ethanol=10:10:5. In element analysis, the diclining of oxygen in all the upper layers and the increasing of nitrogion in both layers of (NH4)2SO4 system indicates the abbility of the less oxygen components concentration of the ATPS and the reaction between (NH4)2SO4 and SBO. According to FTIR test, the lack of absorption at 1515cm-1 of all the lower layers indicates the completely transforming of phenols into the upper layers. Because of the high extraction rate and less influence to SBO, ethanol/NaH2PO4 system may be the most suitable ATPS for SBO extraction.