A microspheric ionomer having a cross-linked structure, a preparation method therefor, applications thereof, and a preparation system thereof. The ionomer comprises structure units A represented by formula (1), structure units B represented by formula (2), and a cross-linking structure provided by a cross-linking agent, M being separately selected from H, a metal cation, and a straight chain, a saturated alkyl of branched or ring-shaped C1-C20, R being H or a methyl; and metal cations are introduced to part of structure units A in the ionomer. The ionomer shows an outstanding effect on nucleation of PET, serves as a nucleating agent for PET modification, so as to obtain a corresponding PET composition. A system and method for continuously preparing maleic acid ester ionomer microspheres and cross-linked maleic acid ionomer microspheres, so as to achieve continuous preparation, washing and separation of ionomer microspheres, effectively stabilizes the separation effect, and avoids frequent start and stop operations of a centrifuge.