Abstract: The kerosene dilution method for determination of density of heavy viscous oil was improved in three aspects. First, random weighed kerosene and heavy viscous oil was mixed, instead of equal volume mixing method. Second, a digital analyzer consisting of a U-shaped oscillating sample tube was used to replace the manual hydrometer method. Finally, a computational formula for viscous oil density determination were programmed and installed into the computer, by which the viscous oil density can be automatically and quickly determined through directly entering four parameters. It is found that the mixture of kerosene and heavy oil closely obey the volume additivity rule and within (1:2) ~ (2:1) mass ratio scope of heavy oil and kerosene, the density of heavy oil can be obtained satisfactorily by the modified method. The standard deviation for three times density determination is less than 0.000 1 g/cm3, parallel to the result of direct oscillating U tube method, but superior to hydrometer method. The modified method is also suitable for heavy crude oil containing bubble.