Abstract: The inner macrostructures adjacent to the thermocouple node in the samples of cast iron thermal analysis were studied. The experiments indicated that the serious macroporosity, which is around the thermocouple node, often exists in the thermal analysis samples so that the accuracy of Si content predicted by thermal analysis device is reduced. The quartz glass tube and Te content added have no effect on the inner macroporosity, but when the taper of the sample cup is increased, the macroporosity area can rise away from the vicinity of the quartz glass tube and the inner macrostructure near the thermocou-ple node will be sound and homogeneous.