A Stirling Engine is a mechanical device, which operates on a closed regenerative cycle, based on cyclic compression and expansion through a piston and a displacer respectively. It can be widely used for many thermodynamic purposes such as stationary power generation, heat pumps or co-generation systems. Due to the external supply of heat and increasing scope of solar energy utility in Pakistan, this engine can be operated successfully with this useful source of energy. Phase angle is an important parameter of the Stirling engine and is one of the key factors on which performance of the engine depends. It is the angle by which expansion space volume leads the compression space with respect to the volume variations in the engine cycle. This paper describes the optimization and modelling of the phase angle of a single cylinder beta Stirling Engine with Helium as the working fluid. Schmidt analysis is considered to be the standard during this research for analysing the output efficiency of the engine. The volume and pressure variations are computed at different values of phase angle for a complete cycle and ultimately values chart and pressure-volume diagrams are prepared. The work done for each case is calculated for finding the optimum phase angle. It is calculated that the best suitable phase angle for the maximum efficiency of the engine is around 90°. Along with maximum and minimum pressure inside the engine, the overlap volume in beta type Stirling engine plays a vital role and efficiency increases with increase in overlap region.