The effects of n-butanol content and oil-water ratio on the microemulsion phase behavior of diesel oil and distillate oil at 350~395℃, 395~450℃ and 450~500℃ were investigated using isoctyl polyoxyethylene ether-5 (E1305) as surfactants. The results showed that the phase of microemulsion system changed from Winsor I →Winsor III →Winsor II with the increase of n-butanol content.The optimum solubilizing parameter (SP*) decreases while the optimum alcoholicity (A*) increases with the increase of oil phase distillation temperature. For the system with low contents of N-butanol and E1305, the phase changes from micelle solution type → Winsor-like II → Winsor IV→Winsor I with the increase of oil-water ratio. For the system with lower n-butanol content and higher E1305 content, the phase changes directly from micelle solution to Winsor I microemulsion with the increase of oil-water ratio. For the system with higher n-butanol content, the phase states change from Winsor II →Winsor III →Winsor I with the increase of oil-water ratio. The oil-water ratio required for phase transformation is related to the surfactant content and the distillation temperature of the oil phase.