The water solubilization of the microemulsion system composed of TritonX100, different co-surfactant and oil are investigated. The effect of temperature, pH value on the stability of the systems are studied. The pseudo-ternary phase diagrams in quaternary microemulsion systems of TritonX100 are measured. The results showed that when the mass ratio of TritonX100 to isoamyl alcohol is 1:1, and the mass ratio of both TritonX100 and isoamyl alcohol to n-heptane is 4:1, the most water solubilizing capacity in the TritonX100/isoamyl alcohol/n-heptane/water system is 50%. Its stability region has increases along with the temperature increment below 80℃. The influence of pH value for stability of the system is less.