This paper describes the preliminary results of a study focused on the semi empirical modeling of an excavator's hydraulic pump. From the viewpoint of designing and tuning an efficient control system, the excavator is a very complex nonlinear plant. To design and tune such a complex control system an extremely good nonlinear model of the plant is necessary. The problem of modeling an excavator is considered in this paper; a nonlinear mathematical model of an excavator has been developed using the bond graph methodology realized in the AMESim® simulation software to replicate actual operating conditions. The excavator model is described by two models: a hydraulic model and a kinematic model. At this stage of research the hydraulic model deals solely with the model of the main hydraulic pump, which has been conceived as a semi empirical model. The pump model has been conceived as a grey box model; where the flow compensator and pressure compensator have been modeled as white box models while the actual flow characteristics of the pump as a black box model. The other excavator hydraulic system components comprising of valve block and actuators have been created using generic mathematical models. This approach has been followed to enable the study of the pump's dynamic behavior and interaction with a completely developed kinematic model of the excavator. Dynamic loading of the system has been realized through a 2D kinematic model of the excavator's body elements. The kinematic model comprises of the boom, arm and bucket whilst their respective motions have been defined for a cycle of operation. The dynamic parameters of each element are continuously calculated during an excavation cycle, thereby providing a platform to study the pump's behavior. At this phase of model development the semi empirical model of the variable displacement pump has been validated on the basis of a set of experimental data collected on a test rig at particular experimental operating conditions. The final objective of this study would be to develop a complete mathematical model of the Excavator Hydraulic Control System and in turn facilitate the study of alternate control strategies towards energy efficient systems. This paper presents the results of this study.