Abstract: Oil compatibility is the important factor which influence the quality and stability of mixed oil.The study about unsaturation and compatibility of binary mixture system ( LO and RO/SBO/CNO) was researched by the detection of iodine value and the map of solid fat content isotherm curve ( SFC-T) or the deviation curve ( Δ SFC-T) .At the same time, the basic physical and chemical properties of lard oil ( LO) , rapeseed oil ( RO) , soybean oil ( SBO) and coconut oil ( CNO) were analyzed.The results showed that the unsaturation of oil which mixed with LO and RO/SBO/CNO was increased with the mass fraction of RO/SBO and showed positive correlation, while CNO was the opposite. The mixed oil present mild eutectic phenomenon appeared in 5/10 ℃ and monotectic phenomenon in 15 ~ 50 ℃. RO and SBO had better compatibility with LO, CNO was the worst.The best mix proportion were 1∶ 9 ( RO∶ LO) , 1∶ 9/2∶ 8 ( SBO∶ LO) and 1∶ 9 ( CNO∶ LO) , and all the value of Δ SFC were in the range of-1.5% ~2%.