Grafted polymer layer composed of a binary mixture of incompatible chains under good solvent condition is simulated using the bond-fluctuation model. The equilibrium structures of the partially phase separated states are investigated as a function of the incompatibility and relative fraction by monitoring the monomer distribution functions and the chain linear dimensions. For the case of symmetric binary mixtures, we observe the chains of the same type cluster together laterally forming the "ripple state" while the layer state is never observed. For asymmetric mixtures, layer structures with the minority chains staying further away from the grafting plane are observed which is in contrary to previous theoretical predictions. The heights of both the minority and majority chains in the layer state are shown to be proportional to their chain lengths.