We studied the phase separation of grafted homopolymers of two different kinds (A and B) under strong demixing interaction, with demixing energy far greater than kT per chain. We successfully constructed a stable self-consistent model for the phase-separated state will all the chains end at the same height. The configuration contains pure A and B monomer regions and inevitable A-B mixed regions. We studied the composition and magntitude of the free energy of the system, calculated the size of the periodic regions and its dependence on the demixing interaction strength. The system with distributed end density profile is further studied. Comparison is made with results obtained from the previous weak interaction model using second order correlation function under mean field approximation