Abstract: The content of diamondoids in crude oils of different density from the Junggar Basin was analyzed by gaschromatography-mass spectrometry-mass spectrometry to investigate the effect of group component separation and direct injection on the determination of diamondoids in crude oils. The group component separation method will result in the loss of adamantane from crude oils, especially a large loss of single adamantanes with relatively lower density. However, the group component separation method is conducive to the enrichment of low-mass adamantane compounds in low-maturity crude oils, especially the diadamantane compounds which are less affected by volatilization, and thus more favorable for detection. The group component separation process has little effect on the isomerization index of adamantane, but has a great influence on the concentration index. Therefore, in order to reduce the loss of diamondoids during preparation, complex pretreatment should be avoided as much as possible. The direct injection method is the best pretreatment method for the determination of adamantane compounds in normal oils, light oils and condensates. For some low-maturity crude oil samples, the group component separation method can be considered.