A fast coalescence mechanism is proposed to account for the wall effect on the formation of gradient morphologyin phase separated polymer blends during quiescent annealing. The existence of solid wall with high polarity is believed tochange the potential field around the dispersed pedicles near the wall. This additional potential interaction between the solidwall and the dispersed particles causes faster coalescence of the dispersed particles near the wall than in the bulk. The gradient phase morphology thus formed can be predicted by combining the wall-particle interaction and the touch-coakescence mechanism.The effect of interfacial tension on the gradient morphology is also discussed.