A fluid sterilizing device includes a first reaction chamber, a second reaction chamber, a communication chamber and a light source. The first reaction chamber is connected to a fluid inlet. The second reaction chamber is connected to a fluid outlet. The communication chamber is connected the first reaction chamber with the second reaction chamber. The light source is configured to emit sterilization light to enter the first reaction chamber and the second reaction chamber. The fluid inlet allows a fluid to enter the first reaction chamber, the communication chamber allows the fluid to pass through and enter the second reaction chamber, and a flow velocity distribution of the fluid in the second reaction chamber is different from that of the fluid in the first reaction chamber.