The invention belongs to the field of building materials, and relates to an activator for rapid hydration of type II anhydrous gypsum and a rapid hydration method. The activator comprises the following substances: an active activator, dihydrate gypsum seed crystals and an aqueous solution. The rapid hydration method comprises the following steps: step 1, grinding anhydrite for 30 min or more untilthe specific surface area is not less than 500 m<2>.kg<-1>; (2) weighing the anhydrite, the active activator, the dihydrate gypsum seed crystals and the aqueous solution according to the formula, feeding, and stirring at 0-42 DEG C for 24 hours; (3) after a set hydration end point is reached, stopping hydration of a hydration product with absolute ethyl alcohol, filtering with fast filter paper,and washing with absolute ethyl alcohol for 2-3 times; and (4), drying the washed hydration product in a vacuum drying oven at 45-50 DEG C to constant weight, measuring the content of crystal water, and calculating to obtain the corresponding hydration rate. The rapid hydration method can realize rapid hydration of gypsum, and is energy-saving and environment-friendly.