A computer system includes an enclosure, a printed circuit board, and an airflow guiding duct. The enclosure includes a bottom plate. The printed circuit board is mounted on the bottom plate. The printed circuit board includes a first heat generating element and a second heat generating element. The airflow guiding duct includes a top wall, a first sidewall, a second sidewall, a first mounting wall, and a second mounting wall. An input opening is surrounded by the top wall and the first and second sidewalls. A first output opening corresponds to the first heat generating element, and is surrounded by the top wall and the first and second mounting walls. A second output opening is defined in the second sidewall corresponding to the second heat generating element. An obtuse angle is defined between the second sidewall and the second mounting wall.