This paper reports the analysis on thermal performance of an earth tube by a computer simulation based on the three-dimensional finite difference method. The computer simulations are divided into two phases. Firstly, the influence of various factors on the earth tube performance is systematically analyzed. Influencing factors include the length, the depth and the diameter of the earth tube, and the airflow volume. Secondly, the effects of climatic conditions and operating conditions on performance of the earth tube over a period of three years are calculated using standardized weather data.