Conduction band structure of K3C60 single crystal films was studied at temperatures near 200 K. Band dispersions along the 111 direction could be observed at 190 K using synchrotron radiation photoemission spectra technique. When the sample temperature increased to 220 K, most subpeaks of the conduction band vanished and the dispersions could not be observed. This result coincides with the existence of an orientational phase transition occurring at 200 K. The fcc nearest-neighbor antiferromagetic Ising model was adopted to analyze the temperature dependence of the band structure. The phase transition is due to the one-dimensional-disordered structure (1DDS) at lower temperatures, which turns to a mixture of bi-directional structure domains and disordered molecules at higher temperatures. The number of disordered molecules was deduced to be about 40 percent of the total molecules at 220 K.