The present invention provides a composition of a polyethylene glycol maleimide derivative and a polymerization inhibitor. In particular, the present invention provides a composition of an 8-arm polyethylene glycol maleimide derivative and a phenolic polymerization inhibitor. The ingredient and content of the polymerization inhibitor in the composition are reasonably chosen, thereby significantly increasing stability of the polyethylene glycol maleimide derivative, effectively avoiding the undesirable effect of gel solidifying due to polymerization during storage and transportation, and extending a pot life and shelf life of a product thereof.