The invention is a UV sterilizing box structure. A box body has a round chamber, an inlet, and an outlet. The round chamber is formed with an arc-shaped guiding channel. A UV light module is disposed on a side of the box body. An external fluid enters the round chamber via the inlet and spirally flows through an inside of the round chamber along the arc-shaped guiding channel so as to make the fluid in the box body generate a flow with a specific direction and stay for enough time to be sufficiently irradiated by UV rays. Thereby, a better effect of sterilization may be obtained.