The invention discloses a crab weighing device. The device comprises a container used for accommodating a crab. A top of the container possesses an inlet which the crab is put into. An internal bottom wall of the container is a curved surface which is gradually concaved downwardly along a direction from a periphery to a middle portion. The container is provided with a folding structure. When the folding structure is opened, the crab can be taken out. The top of the container is provided with a hook component where a weighing hook can hang. When the device is used to investigate and measure the crab in a river, a lake or a pool and the like, an interference of an extraneous environment factor can be reduced, and damages to the crab because of manual factors are decreased so that a measurement result is accurate and investigation is meaningful.