Bioremediation is now a promising way to treat oil-polluted soil. In this paper, the author arranged the 7 main factors influencing the bioremediation found in former experiments on 16 samples with the help of orthogonal table and performed a series of experiments. The relative weights and optimal levels of these factors are found; the fates of different components in oil during the late phase of the bioremediation are studied; the structure differences among the residues are analyzed. The 7 factors influencing the bioremediation of oil-polluted soil are： pollution intensity, nutrients (NH₄NO₃, K₂HPO₄), oxidant (3%H₂O₂ Solution), surfactant (TW80), temperature, water ratio and soil disturbance. The weights and optimal levels of factors can change during different phases of the bioremediation. In the late phase of the bioremediation, the main residues of oil pollutant are n-alkanes and isomeric alkanes. The spectrogram of n-alkanes changs from a symmetrical bell shape to an unsymmetrical bell shape. The proportion of isomeric alkanes increases and the base line from C15 to C21 is driven up.