The comparative experiments of phytoremediation, microbial remediation and plant-microorganism combined remediation of outdoor dotted plant for different contents of diesel contaminated soil were carried by using mixed strains of petroleum hydrocarbon degrading bacteria and two kinds of plant (alfalfa and tall fescue). The germination rate of plant seeds and plant growth status in phytoremediation and plant-microorganism combined remediation experiments were studied, and the degradation effects on diesel contaminated of three remediation methods by ultrasonic extraction ultraviolet spectrophotometry were analyzed. The experimental results show that diesel oil delayed the germination time of plant seeds. The plant biomass and plant height of tall fescue are greater than that of alfalfa in the process of phytoremediation and plant-microorganism combined remediation. As a whole, the plant biomass and plant height of plant-microorganism combined remediation are significantly higher than that of phytoremediation. The sort of overall degradation effects of three remediation methods for diesel contaminated soil are as follows: plant-microorganism combined remediation, microbial remediation, phytoremediation. The remediation effect of tall fescue is better than that of alfalfa. The lower diesel concentration of diesel contaminated soil would make the remediation effect better.