Plasticizers are widely present in water and soil environment, and they can bring enormous threats to environmental safety and human health. A discharge plasma system driven by a high-frequency electric source was used to remove the plasticizer from wastewater; and dimethyl phthalate (DMP) was chosen as the representative of plasticizer. DMP elimination performance at various operating parameters, roles of active species in DMP degradation, DMP decomposition process, and its residual toxicity after decomposition were systematically investigated. The experimental results demonstrated that almost all of the DMP and 80.4% of the total organic carbon (TOC) were removed after 30 min of treatment. The DMP decomposition process fitted well with the first-order kinetic model. Relatively higher applied voltage, lower initial concentration, and alkaline conditions favored its decomposition. •OH was the decisive species for DMP decomposition, in addition to •O and O; while the role of hydrated electrons was negligible. The analysis of DMP decomposition process showed that the molecular structures of the DMP were destroyed, and 3-hydroxy-dimethyl phthalate, monomethyl phthalate, and phthalic acid were detected. Furthermore, the residual toxicity after DMP decomposition was analyzed via seed germination and photobacterium bioassay.