Dry Strength Agent with net structure is the copolymer of acrylamide, its large molecule chain has zwitterion functional group which have strongly the anti-jamming ability to impurity ions. It can improve the ring crush strength, tensile strength, bursting strength and interlayer bindings force, meanwhile, it has good performance in retention and drainage. It has stable strengthen effect even if papermaking condition changed (PH, Aluminum sulfate and pulp).Besides, under closed system (circulation use of water), especially high temperature conductivity, it still can keep the high strength effect.