Dimers are low molar mass LC molecules consists of two identical rigid rod like structural molecule called mesogen jointed by highly flexible alkaline core spacer that provide the necessary mobility with in the LC phase. The phase transition behavior of LC dimers are strongly depend on the length and parity of the flexible spacer, the nature of its link to the mesogenic group and external filed. MC simulation techniques has been utilized, in order to understand the phase transition behavior of varying spacer LC dimers. A tractable coarse grained force filled dimer model has been used for internal Dimeric and monomer- substrate interaction at isobaric- isothermal (NPT) ensemble of system, confined in a slit pore made of two parallel impenetrable flat wall of Homeotropic anchoring by applying potential interaction of Gay Bern and LJ particle. LC dimers are coarse grained as a collection of spherical bead and ellipsoidal mesogen corresponding to virtual bonding at junction with variable bond length to preserve the architectural connectivity to sample available free volume in the interior of dimers. The structural and alignment properties of Dimer of three varying spacer (Sp3, Sp 5 and Sp7) in two different substrate- Dimer interaction system at different thermodynamic state point are simulated and investigated to analyze the effect of surface of the confining wall, spacer and pressure. The simulation result show that there is significant structural and alignment change in LC dimer model system driven by the surface anchoring strength, spacer (alkaline chain length in between rigid molecules) and pressure. The surface nature induce unique submolecular partition of dimer segment (bead/mesogen) along the slit. In mesogen phobic surface, wall are attractive to the mesogenic unit and repulsive to spherical bead ,mesogenic unit put in the immediate vicinity of substrate in each varying spacer. However in bead phobic surface, wall attractive spherical bead and repulsive to mesogenic unit, spacer bead put in the immediate vicinity of surface. The spacer increase in between dimer molecule create segregation of mesogen from the surface to the bulk and develop layer. This transmission or propagation of layer in different wall interaction is not uniform in the aligning direction. LC dimer having sp3 at high pressure have better crystallinty in the confining wall and formation of clear smectic A phase system. The pressure increase