Abstract: Radich method used to measure saturated vapor of ·gasoline has been applied for measuring that of crude oil. The error is proved to be rather serious.A new method called Reference Method has come into being of measuring crude saturated vapor using Radich measuring principle and the instrument. It provides higher accuracy than that being used in foreign countries, therefore it was approved to be a national stardard. Through analysis on the measured data, it was found that there is a linear correlation between crude saturated vapor and temperature, which can be expressed with the Lockhart-Martinelli empirical equation; Lnp=B+A/T, which shows that the samples got in different time will have different saturated vapor pressures.