A fluid sterilization device includes a first reaction chamber, a second reaction chamber, a communication chamber and at least one light source. The first reaction chamber is connected to a fluid inlet. The second reaction chamber is connected to the fluid outlet. The communication chamber connects the first reaction chamber and the second reaction chamber. The light source is configured to emit a sterilization light to 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 then flow to the second reaction chamber, and flow velocity distribution of the fluid in the second reaction chamber is different from that of the fluid in the first reaction chamber.流體殺菌裝置包括第一反應腔、第二反應腔、連通腔及光源。第一反應腔連接至流體入口。第二反應腔連接至流體出口。連通腔連接第一反應腔與第二反應腔。光源用以發出殺菌光至第一反應腔與第二反應腔。其中，流體入口允許流體進入第一反應腔，連通腔允許流體通過而進入第二反應腔，流體在第二反應腔內的流速分布不同於流體在第一反應腔內的流速分布。
