Steel structures is widely used for construction due to high strength with high ductility. There are many types of steel structure, one of the most popular which used now is castellated beam. Castellated beams are those beams which has opening on the web portion. Castellated beam are used to pass underfloor services ducts (i.e water and sewage pipes, air ducts, cables, etc). Considering structural performance of the beam, opening angle and spacing between two openings is important concern. Therefore, in this paper, numerical modelling approach is used for determining opening angle and spacing between to openings on hexagonal castellated beam. The finite element model was developed using ABAQUS/ CAE version 6.11 and the Von-misses failure criteria was used to find out the failure load on the beam. Three variations angles (50o, 60 o, 70 o) with different opening spacing (6 mm, 9 mm, 12 mm) have been used (6 mm, 9 mm, 12 mm). Result showed that, the opening spacing and opening angles which gives better result is 6 mm and 60o with load at yield is 78.4812 kN, deflection at yield is 0.7867 mm, and von-misses stress is 247.4 MPa. There is no significantly different between the numerical model and the experimental model, the difference mean of the model is ±10%. Due to almost of the tee-section (web-post) of the beam is yield, the Vierendeel failure mechanism took place.