The temperature profile and infrared exitance of a terrain object were calculated by combining domain decomposition method with monte carlo method. The object with 3 D complex shape can be divided into several regular sub zones, which are described by corresponding coordinate systems. The heat transfer within every sub zone was calculated by control volume method and the heat transfer among sub zones calculated by thermal mesh method. When the radiative transfer coefficient (RTC) was calculated by means of monte carlo method, the complication of surface radiative characteristic could be taken into account.By application of the RTC, a complicated calculation can be divided into several relatively easy sub calculations, and the calculation in several different wavelength bands can be solved parallelly.In space zone (computing zone),the object was divided into a number of domains, then several processors were used simultaneously.