The invention provides a pyridineless esterifying reagent which is used in anhydrides method for measuring polylol hydroxyl values. The reagent comprises anhydrides, an oxygen-metal complex with a formula of MomLn and a solvent of neutrality or subacidity, wherein, M includes a transition metal of IVB group, VB group or VIB group; L includes (OTf), X, or m and n are integers equal to or greater than 1, wherein, X is halogen; R, R', R'' and R''' are respectively alkyl, aryl or heterocyclic radical containing nitrogen, oxygen and phosphorus or sulfur. The invention also provides a method for measuring the polylol hydroxyl values.