The invention relates to an extra-large fiber reinforced plastic (FRP) combined storage tank structure with a floating roof, and a construction method of the storage tank structure. The extra-large FRP combined storage tank structure comprises a tank top, a tank wall and a tank bottom, wherein the tank top has an FRP latticed shell structure; FRP plates are laid on the FRP latticed shell structure; the tank wall is composed of an inner layer FRP plate, an outer layer FRP plate and active powder concrete between the inner layer FRP plate and the outer layer FRP plate; the floating roof is arranged in the tank cover; a connection piece is arranged between the inner layer FRP plate and the outer layer FRP plate; concrete trapezoid grooves are sequentially formed between the inner layer FRP plate and the outer layer FRP plate along a circumferential direction; prestress bars are pulled between every two adjacent concrete trapezoid grooves section by section; and the inner layer FRP plate and the outer layer FRP plate are formed by connecting FRP spliced plates through tenon tongues and tenon grooves. The extra-large FRP combined storage tank structure is high in corrosion resistance and freezing resistance, insensitive to temperature change, low in heat transmission speed, favorable for keeping temperature in a tank body, high in compression strength, high in corrosion resistance and relatively high anti-permeability.