The present disclosure relates to the technical field of wastewater treatment in oil and gas field operations, in particular to a method for synergistic degradation treatment of polysaccharide-containing polymer wastewater by controllable —OH radical. In this method, a ferrous ion solution, an alkaline solution, and an oxidant solution are mixed and heated to generate —OH radicals, —O radicals and polymeric iron ions, etc., which then is mixed with polysaccharide-containing polymer wastewater. The generated highly oxidative —OH radicals and —O radicals react with polysaccharide polymers so that they are degraded. The generated polymeric iron ions form flocs that purify the suspended solids in the wastewater. The purified polysaccharide-containing polymer wastewater can be re-injected or reused as an oilfield working fluid. In the present disclosure, the polysaccharide-containing polymer wastewater can be treated in a quick and efficient manner, and the treated wastewater can be recycled.