The utility model discloses a phytoplankton siphon device, include: be used for holding the container of water sample, the container has the opening, the fixed setting at the first disk body of the open -ended of container, first disk body are equipped with the guiding hole, and the extending direction of guiding hole is perpendicular with the horizontal facial features in the container, the straw, including hard tube section and hose section, hard tube duan ke slide from top to bottom cartridge in guiding hole, and the lower extreme of hard tube section inserts perpendicularly below the horizontal plane to the container in, the hard tube section is exposed and is equipped with the scale mark on the pipe wall outside the container, the lower end face seal of hard tube section, and the lateral wall that stretches into below the surface of water is equipped with the suction inlet, the fixed second disk body that sets up on the hard tube section is equipped with the partial outer wall of scale mark, float, float on the surface of water of container, and the hard tube section pass the float and with float fixed connection. According to the configuration, the utility model provides a phytoplankton siphon device, it can avoid the stirring that causes phytoplankton, and can effectively improve the experiment accuracy.