Natural astaxanthin has outstanding biological activity and high economic value. However， many studies are still limited to the astaxanthin extraction with organic solvents such as acetone， which causes great pressure on the environment， and reduces the production safety. To explore an efficient and green process for astaxanthin extraction， novel ionic liquid （IL）-based aqueous biphasic systems （ABSs） were constructed. The effects of IL， temperature， pH on the phase behavior of the ABSs and astaxanthin distribution were investigated. The results showed that tributyloctylphosphonium bromide （[P4448]Br）， tributyloctylphosphonium chlorine （[P4448]Cl）， tetrabutylphosphonium bromide （[P4444]Br）， tetrabutylphosphonium chloride [P4444]Cl， tetrabutylphosphonium trifluoroacetate （[P4444]CF3COO）， and tetrabutylammonium bromide （[N4444]Br） could form low critical solution temperature （LCST）-type ABSs with K2HPO4/KH2PO4. [P4448]Br has the strongest ability to form ABS and the [P4448]Br-based ABS showed the highest extraction yield of astaxanthin. When the ultrasonic power of 75 W and ultrasonic time of 60 min， the extraction yield of astaxanthin in obtained from Haematococcus pluvialis by [P4448]Br-K2HPO4/KH2PO4 ABS was 96.09%. The results help us to understand the correlation between the phase behavior of the ABS and the extraction of biomolecule， and provide an important theoretical basis for the astaxanthin extraction from bioresources.