The invention discloses an advanced treatment technology of petrochemical wastewater. A composite treatment agent prepared from modified starch, siliceous carbonate, aluminium hydroxide, polyferric sulfate, polysilicon aluminum sulfate, calcite powder, opal powder, sodium hypochlorite, poly-aluminum calcium chloride, sodium hydroxide caustic soda flakes, glacial acetic acid, 3-Oxo-1-cyclopentanecarboxylic acid, potassium ethylate, pilocarpine and a coagulant aid. The composite treatment agent is matched with corresponding water treatment technologies including adsorption, treatment agent treatment, anaerobic treatment, photo-catalytic oxidation, sodium hypochlorite oxidation, aeration, electric flocculation, electroflotation and the like, so that COD, the oil content, the benzopyrene content and chroma of treated wastewater are obviously reduced, the requirements of environment protection standard can be met, and application prospects are good.