Qualitative analysis of residual gases in fully sealed 4 in. color field emission display (FED) devices has been performed utilizing a home-made mass spectrometer. Relative molecule mass for each gas was measured as a function of time during an exhausting process. A real 4 in. panel experimentally exhibited several gases, such as H2O, H-2, OH, CO, N-2, and CO2, etc. Partial pressure of each residual gas was calculated as a function of exhausting time, resulting in an estimation of total pressure in a real panel. In addition, for simple comparison, vacuum properties inside the panel were analyzed using a Monte Carlo method, based on molecular flow conductance inside it with an exhausting pipe. Transmission probability of molecules at various geometrical and temporal parameters was simulated for pressure optimization inside the panel during exhausting. The results were used to calculate the pressure of the FED panel, resulting in comparison with experimental values. It would provide the basis in future design and fabrication of real FED panel.