Effects of phase change in the recording layer due to temperature changes and the material parameters used in the simulated transient temperature distributions were examined. The initial structure of the recording layer was the key parameter for simulated temperature distributions in both the erasing and writing processes. Latent heat due to the phase change had little effect on the transient temperature distributions, however, the temperature-dependent heat capacity had significant effects and resulted in a transient temperature distribution level lower than that using a constant room-temperature capacity value. From the simulated transient temperature profile, cooling rate, dependence of phase-changed spot size on the laser power and laser pulse duration, as well as the phase-change characteristics in the phase-change optical disk, could be obtained. By applying proper material parameters, the disk with a hydrogenated amorphous carbon film as the top dielectric layer with a disk structure of PC/ZnS-SiO2(111nm)/GeSbTe(20 nm)/α-C:H (63 nm)/Al(70 nm) showed less temperature variation between the center and the edge of the irradiated spot than that of a disk with a conventional disk structure of PC/ZnS-SiO2(144 nm)/GeSbTe(20 nm)/ZnS-SiO2(21 nm)/Al(70 nm). Less temperature variation may give rise to a written spot with more uniform microstructures.