Crosslinking degree is one of the important properties of styrene resin. It is the network structure of the framework of ion exchange resin polymerized by various organic materials, expressed in percentage. Crosslinking degree refers to the mass percentage of divinylbenzene (commonly known as "crosslinking agent") contained in styrene resin. That is, if the crosslinking degree=divinylbenzene mass/(styrene mass+divinylbenzene mass) * 100% resin has low crosslinking degree and good water swelling property, the resin has large cross-linking mesh and fast exchange rate, but low resin strength. On the contrary, when the cross-linking degree of the resin is high, its cross-linking mesh is small, the resin strength is high, and the large volume of ions entering the resin during exchange is limited, which improves the exchange selectivity, but the swelling of water is poor, and the reaction speed is slow. The cross-linking degree of styrene resin used for chemical water treatment is generally between 4-14%, and the performance is ideal when the cross-linking degree is about 7%.