The invention discloses a floating anchor chain expandable settling particle catching device, which comprises a floating system, an offshore warning and positioning system, an anchor chain system anda counterweight system. At least one expansion unit is connected with that anchor chain system, and the expansion unit comprises an expansion pipe arm and an expansion device. The expansion pipe arm comprises a bracket, a support ring and an annular buckle, wherein the expansion pipe arm comprises a bracket, a support ring and an annular buckle. The support comprises a hollow upright post and a support arm, wherein the upright post jacket is provided with at least one support ring, the support ring and the upright post are connected with each other through the support arm, a plurality of ringbuckles are arranged on the support ring, and the ring buckles are symmetrically arranged around the outer wall of the support ring; The expansion device is arranged on an annular buckle, and comprises a sediment capture device, an image acquisition device and a culture device, and is mainly used for sedimentation particle collection, in-situ cultivation, data acquisition and measurement, etc., and is of great significance in the research of the global marine carbon cycle and the biological pump.