The invention discloses a rotary bank-off advancing type riverbed deposit sampling device under a self-weight effect. The device comprises a liftable operating platform, a power system, a transmission rod and a sampling tube system, wherein the liftable operating platform is fixed to the side face of a surveying vessel; the power system is arranged on the liftable operating platform; the upper end of the transmission rod is arranged in a hole of the power system through a master bushing and is in drive connection with the power system; the lower end of the transmission rod is connected with the sampling tube system; the power system transmits a shear force to the sampling tube system through the transmission rod; the self-weight of the whole transmission rod and that of the sampling tube system are adopted as drilling pressure to drill to a sampling position, and finally the whole sampling tube system is lifted to the surveying vessel to complete sampling work. The device is simple in structure, convenient to disassemble, and suitable for deepwater sampling in a water reservoir, and can prevent a deposit sample from being disturbed.