This paper study about the analytical behaviour of Concrete beam encased with Steel castellated beam as composite member with various web opening section of the castellated beam as optimization of section by its maximum Load carrying capacity and deflection. The modelling and Finite Element Analysis was done using Ansys Workbench 16.2. The Concrete beam having section size of 150mm x 170 mm x 1500mm encased with Structural Steel ISMB100 of span 1400mm is used for castellated beam for various shape of web opening are provided. The parametric study has shown the Deflection and Load carrying capacity of the various cross sectional beams with Hexagonal opening (inscribed in the circle 25mm radius) which has high load carrying capacity and the less deflection while compared to the other sections of circular web opening (25mm radius), hexagonal wide web opening (25mm with 1:1:1 web ratio), and rectangular web opening of (25mm x 50mm). Alternate incremental loading is applied by using Ansys workbench 16.2 and results and graphs are plotted.