A passive ventilation system of solar chimney combined with earth cooling is investigated numerically in this study. The effects of the solar chimney height and air gap width are examined together with a fixed earth cooling duct under different climate conditions. The earth cooling duct has a length of 17 m and is buried at a depth of 3 m with an assumed soil temperature of 22°C. With the average monthly solar radiation and ambient temperature for a city picked in Texas, the ambient air entering the room can be cooled down from 29.2°C to 22.5°C in August and heated up from 16.2°C to 20.3°C in February. A flow rate of 0.029 m³/s is obtained with a solar chimney of 2.5 m tall in August. The ventilation rate is actually higher in February than the others due to the low ambient temperature. The height variation is achieved by extending the chimney of the baseline case in both upward and downward directions. It is observed that the flow rate increases linearly with height in the upward direction but it is not the same in the downward direction. The ventilation flow rate increases by 100% as the chimney height increases from 2.5 m to 4.75 m, while the air gap width has very little impact on results. It is also noted that due to the thermal energy or heat stored in the brick, the air flow can be continued when there is no radiation for hours.