Abstract: The properties of heavy crude oil is described and the effectiveness of diluting and viscosity reduction for heavy crude oil with naphtha-Methyl Ethyl Ketone (MEK) is analyzed. The process of recoverable naphtha with Methyl Ethyl Ketone (MEK) to dilute heavy crude oil is introduced. It is pointed out that although the process of recoverable naphtha with Methyl Ethyl Ketone (MEK) involves one set of MEK recovery unit installation compared to the single naphtha recovery unit without MEK, which will result in higher investment and operating cost, transporting capability of heavy crude oil will be remarkably increased with lower diluting ratio and satisfactory effectiveness for viscosity reduction.