Based on recent applications and research situations of phytoremediation of petroleum contaminated soils, phytoremediation mechanisms of petroleumcontaminated soils were analyzed and summarized. First of all, plant roots can directly absorb petroleum hydrocarbons, and use their metabolisms or plant endophytes to remove the pollutants. Once plant roots absorbed petroleum hydrocarbons, they would be stored in the tissues (phytoextraction) by lignification mechanism, or be converted to some intermediate metabolites with low toxicity, CO₂ and H₂O through phytovolatilization or phytodegradation mechanisms. Plant endophytes are closely correlated with phytodegradation, phytoremediation and phytoprotection of petroleumcontaminated soils. And then, root exudates and rhizosphere microbes determine the direction of rhizosphere mechanisms underlying phytoremediation of petroleum hydrocarbons. The rhizosphere, affected by root activities, is a microecological zone. Thus, rhizodegradation is considered as the main mechanism to remove petroleum hydrocarbons from soils. Plant roots can release some exudates or enzymes to the rhizosphere. Enzymes play a key role in degradation of petroleum hydrocarbons. Furthermore, root exudates can provide carbon, energy or cometabolites to rhizosphere microbes so that their numbers and activities are significantly higher than those in nonrhizospheres, which greatly enhance the capacity of biodegradation. Finally, the future directions can be taken from the following aspects in order to provide important and scientific support for future phytoremediation research: (1) the microecological processes of root exudates; (2) finding and building the functional genes; (3) the processes and mechanisms of anaerobic oxidation; (4) the roles and applications of endophytes; (5) using the omics tools to study phytoremediation mechanisms.