The invention relates to the technical field of metal detection, and discloses a portable water body heavy metal detection device. The portable water body heavy metal detection device comprises two air bags and a box body, the air bags are symmetric with the box body as a center, arc blocks are fixedly installed at the tops of the air bags, fixing frames are fixedly connected to the upper surfacesof the arc blocks, and the air bags are connected with the box body through the arc blocks and the fixing frames. Compared with the prior art, the magnitude of buoyancy of the device in a water bodyis changed through the volume change of the air bags in water, so that the detection depth of the air bags in a polluted water body is adjusted; and meanwhile, by arranging a power device, thrust is provided for the device, the detection range of the device is increased, the air bags and the power device cooperate with each other, so that the device performs online detection at any place of the polluted water body, the sample sampling time is shortened, the detection efficiency is effectively improved, the number of detection is increased, so that more detection data are obtained, comparison is effectively formed, and the detection precision is increased.