A polymer, a polymer electrolyte and a lithium ion battery are provided. The polymer includes a main chain and side chains of the polymer, the side chains contain conjugated cyclic groups and epoxy multi-element cyclic groups; the conjugated cyclic group is selected from saturated or unsaturated C10-C20 conjugated aromatic groups; the epoxy multi-element cyclic group is selected from saturated or unsaturated C3-C8 epoxy multi-element cyclic groups; the main chain of the polymer is selected from polyalkoxy ether. The polymer, the polymer electrolyte and the lithium ion battery can improve interaction between the polymer electrolyte and an active substance in an electrode plate, increase the adhesion of the polymer electrolyte, avoid detachment occurring at an interface between the plate and the electrolyte, and improve the interface stability of the battery.