The peritectic melting of alpha ->beta + liquid is of great importance in various fields. Here by high temperature optical microscopy, the peritectic melting evolution was in-situ investigated, where the alpha phase is the YBa2C3O7-y film deposited on single crystalline substrates and the beta phase is the Y2BaCuO5 grain. A variety of thermal stabilities of alpha films associated with forming behaviors of beta grains were observed, which were mainly attributed to two factors. One is the film microstructure as an internal origin. The other is the driving force supplied by a heating up process as an external condition. More distinctively, analogous to the growth kinetics in crystallization, we derived peritectic melting kinetics of thin films relating to the beta formation. The correlation among film microstructures, driving force and melting behaviors was well established. Most importantly, this new approach of the kinetic analysis in the peritectic melting should be universally valid for more film/substrate constructions. (C) 2013 Elsevier B.V. All rights reserved.