This thesis describes the systematic procedure for investigating the performance and the design analysis of the welded structure of a 150-tonne hydraulic press machine. This machine was designed by ENERPAC without any measurment or variable hydraulic system. The investigation discusses the theoretical and experimental model of the machine to establish the accurately optimal design analysis and further development of the present machine at minimum time and lower cost. The applicability of the existing PC based FE package, as a computer aided design tool, was also investigated. The theoretical model takes into account both conventional analytical formula and numerical technique, using Finite Element Analysis. The conventional model is based on the simple bending theory using the total strain energy principle for 2D beams. The LUSAS Finite Element software system is used as a tool to establish the theoretically predicted numerical model. This model has been discussed with different factors. The factors considered are: the boundary condition; the mesh density and the type of the element being used. The experimental model was based on the electrical method of processing the experimental results using a personal computer through an appropriate data acquisition. The apparatus of the experimental rig and the flow sequence of a computer program, which has been developed to facilitate the measurment of the load deformation of the machine and the load deformation of the workpiece, were discussed. A comparison has been made between the experimental and theoretically predicted results. A good agreement was found between the finite element and the experimental model. Although the conventional analytical model was in good agreement with the plane frame finite element using beam element, this agreement deteriorated between these models and the experimental models. Also, a comparison was made between the stiffness of the actual present machine and the standard stiffness of a similar machine before and after the theoretical modification and disagreement was found. A new optimal design of the structure of the press was discussed theoretically using plane stress finite element model. The factors considered in this optimal design are the width and the chamfering of the press structure. The stiffness of this model has been compared with the standard stiffness,as a design goal, and as a result of this a good agreement has been found and a practical conclusion has been drawn.