The invention discloses a wastewater treatment device and treatment method aiming at a metal surface treatment plant. The wastewater treatment device aims at the wastewater generated in the process of carrying out deoiling, pickling, surface adjustment and phosphorization treatment on a metal workpiece in the metal surface treatment plant, and comprises an oil separation tank, an adjusting tank, a first pH adjusting tank, a first coagulation reaction tank, a floating tank, a second pH adjusting tank, a second coagulation reaction tank, a first settling tank, a middle water tank, a filtering purification device, a hydrolysis acidifying tank, a contact oxidation tank, a second settling tank, a clear water tank, a dosing device and a sludge concentration tank which are sequentially connected by pipelines. After the wastewater is treated by the wastewater treatment device, 80% of treated wastewater is recycled to a production line, and 20% of treated wastewater is discharged up to the standard after further treatment.