According to the technical scheme, a middle frame structure of a circular vibrating screen comprises a middle frame body; a step clamp is arranged at the connecting part of the lower portion of the middle frame body and a lower frame, a sponge skin is arranged on the inner side of the step clamp, and a screening frame is arranged on the lower portion of the sponge skin; a P-shaped fixing frame isarranged at the end of the screening frame, and the outer edge of the P-shaped fixing frame is covered with a U-shaped rubber skin; the lower portion of the U-shaped rubber skin makes contact with a fixing clamp of a bottom frame, and a restraining ring is arranged on the outer sides of the step clamp and the fixing clamp in a sealing mode; and a discharging outlet is formed in one side of the middle frame body, a material guiding box is arranged in a mode of corresponding to the discharging outlet and closely attached to the inner side of the middle frame body, and extend to the discharging outlet in an obliquely-upward mode, and the bottom of the material guiding box is fixedly connected with the bottom face of the middle frame body. The middle frame structure of the circular vibrating screen has the beneficial effects that the screening effect and efficiency of the circular vibrating screen can be promoted effectively, and the sealing effect of the circular vibrating screen is alsogood.