The invention relates to the technical field of coring tools and provides a floating piston device for coring. The floating piston device comprises a flow splitting connector, a screw rod, a piston rod, a spherical seat connector and a piston body; the spherical seat connector is internally provided with a flow baffling hole with a small middle part and large top and bottom; a sphere body is arranged in the middle of the flow baffling hole; the lower part of the flow splitting connector is fixed in the upper part of the flow baffling hole through a thread; at least one pair of symmetrical flow splitting holes are formed in the upper part of the flow splitting connector along the periphery at intervals; the piston body sleeves the inner side of the lower end of the flow splitting connector; the piston rod is fixed at the upper end of the piston body; thread holes are formed in the piston rod corresponding to the flow splitting holes. The floating piston device is reasonable and compact in structure and convenient to use; By virtue of the device, the safety problems including pressure releasing in an inner barrel pressure holding process can be solved and an unloading tool does not need to be used for filling sealing liquid; the floating piston device can also be used for common coring work only if the piston rod and the piston body are removed, and the labor intensity is alleviated and the time is saved.