In order to investigate the role of rhamnolipid on the degradation of polycyclic aromatic hydrocarbons (PAHs), biosurfactant rhamnolipid produced by Pseudomonas aeruginosa was invested on the degradation of phenanthrene. The result showed that the solubility of phenanthrene have linear relationship with rhamnolipid when below or above the critical micelle concentration (CMC). The concentration of rhamnolipid showed stronger solubility when below CMC than above CMC. Then, Pseudomonas aeruginosa strains treated by rhamnolipid were applied in degradation. The results showed that the growth of bacterium was inhibited when treated with 75 mM (1 CMC) rhamnolipid. However, the bacterial treated with 750 mM (10 CMC) rhamnolipid accelerated the degradation. There was no degradation phenomenon occured without treated with the rhamnolipid. This result showed that the cells could not degradate phenanthrene directly. We can deduce from the experiment that rhamnolipid improve the degradation efficiency by increasing the solubility of carbohydrates. This conclusion is significant for the evaluation of rhamnolipid surfactant in the remediation of phenanthrene contaminated sites.