This paper presents an analysis to predict the gap and contact pressure existence in segment joint used in Solid Rocket Boosters using 3-D finite element (FE) as a general nonlinear problem. The relevant components, the tang, the clevis and pin are modeled individually and assembled. The FE modeling includes O-Rings as integral part of joint, which brings out the deformation of seals and contact pressure (CP) between O-Rings and the casings as a function of external loads. The general purpose FE package ABAQUS for analysis and HYPERMESH for pre- and post- processing are employed. The CP between the O-Rings and the slot walls in the joint depends very much on the material properties. The initial CP induced during assembly of segments is higher for lower ambient temperatures and lower for higher temperatures.