The advantages of a 20-ft container construction include their convenience for transportation, rapid assembly, and low costs. In recent years, containers have been used in various applications, including medical testing, mobile offices, business showrooms, restaurant and dining, and industrial purposes. These applications have contributed to the increasingly diverse requirements for indoor ventilation and positive or negative pressure. To explore the relationship between the negative pressure generation effectiveness and air change rate of low-airflow simple fans in a 20-ft container construction, the experiment was conducted under the conditions of an air change rate of 6–12 T/h and that the container construction did not contain hazardous exhaust gases, hence not using any high-efficiency particulate absorbing filter. The lowest standard for pressure difference was employed (-2.0 Pa). The experimental results revealed that to achieve the minimum pressure difference requirement of -2.0 Pa, the air change rate must be 8 T/h or higher in completely closed rooms and 10 T/h or higher in rooms with an open grille. Moreover, to achieve the negative pressure requirement of -10 Pa, the air change rate must be 18 T/h or higher in completely closed rooms and 30 T/h or higher in rooms with an open grille. Finally, the negative pressure generation effectiveness of a fan decreases with distance; therefore, a fan should be positioned close to the center of a room.