In this work, four immobilized kinds of mixed microorganisms were prepared by uploading oil-degradation bacteria into the cross-linked biodegradable polyacrylamide and sodium alginate mixture supporting material, which were employed for efficient degradation of oily wastewater. The morphology of immobilized microbial pellets was characterized by scanning electron microscopy after 7d and 14d of duration. The components of residual crude oil were determined by gas chromatography-mass spectrometry, and the microbial degradation and evolution of n-alkanes, terpenoids, and steroids were studied. The results show that the oil degradation rate for experimental group I (sample containing 1% crude oil) and experimental group II (sample containing 3% crude oil) reaches as high as 70 and 40%, respectively, after 14d of degradation of saturated hydrocarbon total petroleum hydrocarbons. For different oil components, the degradation degree is in the order of tricycoloditerpanes > homohopanes > norhopanes. The order of the degradation degree of steroids with different carbon atoms is C27 > C28 > C29. In terms of evolution characteristics, it can be seen from the biological evolution parameters of n-alkanes that only a slight degradation for odd-even carbon by biodegradable bacteria was achieved, whereas high degradation for isoprene alkanes was observed. According to the biological evolution parameters of hopane and sterane, hopane C31α β-22S/22S + R and sterane C29α α20S/20(S + R) were all greater than 0.4, that is, they are all strongly degraded by microorganisms.