Space exploration missions and space electronic equipment require improvements in solar cell efficiency and radiation hardness. Triple-junction photovoltaic (TJ PV) cell is one of the most widely used PV for space missions due to it high efficiency. A proper models and simulation techniques are needed to speed-up the development on novel solar cell devices and reduce the related expenses. In this paper we have developed a detailed 3D TCAD model of a TJ PV cell, and calibrated the various (not accurately known) physical parameters to match experimental data, such as dark and light JV, external quantum efficiency (EQE) . A detailed model of triple-junction InGaP/GaAs/Ge solar cell has been developed and implemented in CFDRC’s 3D NanoTCAD simulator. The model schematic, materials, layer thicknesses, doping levels and meshing are discussed. This triple-junction model is based on the experimental measurements of a Spectrolab triple-junction cell by  with material layer thicknesses provided by Rochester Institute of Technology . This model of the triple-junction solar cell is primarily intended to simulate the external quantum efficiency, JV and other characteristics of a physical cell. Simulation results of light JV characteristics and EQE are presented. The calculated performance parameters compare well against measured experimental data . Photovoltaic performance parameters (Jsc, Voc, Jm, Vm, FF, and Efficiency) can also be simulated using the presented model. This TCAD model is to be used to design an enhanced TJ PV with increased efficiency and radiation tolerance. Keywords: photovoltaic cell, triple-junction, numerical modeling, TCAD, dark and light JV.