1. The sterane isomerization maturity parameter and alkylphenanthrene index indicate that the maturity of oil sand is low.

2. The spectrums of sterane and terpane were simulated and compared with some parameters and spectrums of actual mixed crude. A satisfactory result has been obtained.

3. After crude oil alteration, the degree of sterane isomerization reaction is enhanced, and in some samples, the balanced endpoint value of isomerization reaction is exceeded far beyond.

4. The sterane isomerization maturity parameter alkylphenanthrene index indicate that the maturity of oil sand is low.

5. The crude oils of Chang 20 belong to typical immature oil which have odd even predominance and lower ratios of sterane and terpane maturity index.

6. We also bring forward a new method to recognize the different biological source for C29 sterane predominance using organic carbon isotope.

7. The diagenetic stages and diagenetic facies are predicted by modeling the paleotemperature, vitrinite reflectance, sterane isomerization rate and authigenic quartz concentration in space and time.