Through the group composition analysis of the oils in Chepaizi area，it is found that the asphalene components are absent not only in the light oil without degradation，but also in some heavy oils，obviously different from the common heavy oil with higher asphaltene content.According to the asphaltene content，the crude oils in Chepaizi area are divided into four types：the first is the light oil without asphaltene，accumulated lately with high maturation；the second is the heavy oil rich in asphaltene，left from the native heavy oil dissolved by the light oil；the third is the heavy oil without asphaltene，dissolved and migrated with the light oil；the fourth is the heavy oil with medium content of asphaltene，diluted and migrated with the light oil in early stage.The main reason accounting for major asphaltene content difference is the different properties of oil at different migration stage.The normal mature oil developed the heavy oil rich in asphaltene and nonhydrocarbon at early stage，and the dissolving capability of light oil infused at later stage for asphaltene is low，and there is no dissolving and migration at later infusing stage.The regulating function of light oil is the intrinsic factor for the tremendous divergence of the oil character in Chepaizi area.The light oil emerged portrait transformational migration at deep fault in Sikeshu sag，and entered into migration pathway including the heavy oil early stage or without heavy oil separately.The main migration is along the layers at slope place.The selective adjustment of the light oil in migration pathway with heavy oil formed the special phenomenon that the oil distributing is light oil on top and heavy oil down in Chepaizi area.