New geant4 based Monte Carlo software for the COMPASS II experiment at CERN Abstract: The substructure of the nucleon can be described within the framework of generalized parton distributions (GPDs). According to Jis sum rule the forward limit of the GPDs is directly linked to the total angular momenta of quarks and gluons. The exclusive measurement of deeply virtual Compton scattering presents a promising experimental approach. The COMPASS II experiment at CERN is designed to carry out these measurements. A profound understanding of the experimental acceptance and background estimates is key to measure absolute cross sections and can only be obtained with Monte Carlo.This thesis comprises the development of the new Geant4 based Monte Carlo Software TGEANT for the COMPASS II experiment. TGEANT was optimized primarily for the GPD program including a tuning of the electromagnetic shower simulation and a software model of the trigger system but has since been extended to cover all other physics programs. It has become a standard in the COMPASS II Monte Carlo chain and has been used by almost all recent analyses