Fan filter unit and air purification system for dust-free room

An air purification system for a dust-free room, comprising:

• a factory;
• and
• fan filter units (FFUs) connected with the factory;
• wherein each of the FFUs comprises a fan, and a filter screen coupled with an air inlet of the fan;
• an air inlet of the filter screen is further configured with an auxiliary filter screen, and a minimum diameter of dust particles filtrated by the auxiliary filter screen is greater than a minimum diameter of the dust particles filtrated by the filter screen.