The construction of sacha inchi oil microemulsion system was researched. Taking the content of vegetable oil in microemulsion system as the evaluation indexes， the type of oil， surfactants， cosurfactants and assisted oil phase were optimized by single factor experiment. And the pseudo-ternary phase diagram was measured according to the optimal formula. The result showed that 2.5g sacha inchi oil was compound with 1.5g olive oil， with 2g isopropyl myristate as assisted oil phase， 2g PEG400 as cosurfactant， 2g hydrogenated castor oil as surfactant， the microemulsion system with content of vegetable oil 39.53% was received. The content of sacha inchi oil in the cosmetic was effectively improved by the microemulsion system.