We report a superheating phenomenon of YBCO thin film by real-time observation of its melting process under a high temperature optical microscope. It was found that the melting occurred at a temperature up to 50 K higher than the peritectic temperature of YBCO (1010C). Further, a systematic investigation was conducted on superheating mechanism of REBCO film and its correlation with film quality. Moreover, using REBCO thin films as cold-seeds, high performance REBCO bulks were successfully grown in the melt-textured process.