The self-assembly behaviors of A-graft-B copolymer structured fluid droplets on a flat solid substrate were studied by using real-space implemented self-consistent field theory, where the long homopolymer chains were employed to fill the air region surrounding the droplet and the "masking" functions were chosen to fit the geometry of the flat solid substrate. It shows that the soft-confined spacing and substrate-surface affinity play important roles to regulate the self-assembly behaviors of polymer fluid droplets on the flat solid substrate. The microphase transition mechanism of the liquid polymer structured fluid droplet was reasonably explained by considering the wetting behaviors.