An ultrahigh-temperature heating platform (HS1400G, Instec, Britain) on the optical microscope (BX51M, Olympus, Japan) was developed to observe the microcrack propagation of thin-section samples during heating in real time. Singapore Bukit Timah granite rock cores were examined in this study. The granite rock is widespread and one of the major rock formations in Singapore. It shows significant mechanical deterioration under the influence of heat. The rock sample was prepared as doubly polished thin sections of approximately 60 μm in thickness for petrographic analysis and microthermometric observation. Before the experiment, the slide was heated with an alcohol lamp to dissolve the resin, and the thin-slice sample was removed and immersed in acetone to wash the surface glue to avoid affecting the observation. The granite sample was heated in the following heating process: heat from room temperature of 25℃ to 100℃ at a rate of 20℃/min; maintain the temperature for 5 min, as the thin-section sample is sufficiently small to generate a homogeneous thermal field quickly; heat to 100℃, 200℃, 300℃, 400℃, 500℃, 600℃, 700℃, 800℃ and 900℃ successively; finally, reduce the temperature to room temperature at a cooling rate of 20℃/min from the maximum temperature.