The invention relates to a floating disc sealing ring fire extinguishing device and method. The device and method mainly solve the problem that in the prior art, foam liquid enters a sealing ring slowly and cannot quickly extinguish fire. The floating disc sealing ring fire extinguishing device comprises a foam liquid storage tank, a foam conveying pipe, a dry powder tank, spray heads, foam generators and a floating disc, wherein an outlet pipeline of the foam liquid storage tank is connected with the foam conveying pipe, the other end of the foam conveying pipe is connected with the dry powder tank, a top outlet pipeline of the dry powder tank is connected with at least one branch pipeline, each branch pipeline is provided with the foam generators and check valves, the tail ends of the branch pipelines are inserted into the sealing ring, T-shaped injection ports are formed in the tail ends of the branch pipelines, and the distance between the adjacent spay heads in the sealing ring isnot larger than 24 meters. According to the technical scheme, the above problems are solved, and the device can be applied to fire suppression of the sealing rings of a floating roof tank and an inner floating roof tank.