Time-of-flight mass spectrometers (ToF-MS) are instruments of choice for analyzing the mass distribution of elements or molecules constituting various samples. They are particularly suitable for isotopic studies of samples in the nuclear industry as well as for research in materials science or pharmaceuticals [1]. Problem to solve: Typically, a ToF-MS performs ultra-rapid ionization of a portion of the sample to be analyzed and the created ions are extracted and accelerated by electric fields. After that, the ions are released into the free flight section of the instrument where their mass separation occurs. They are detected at the exit of this zone by a high gain ion detector such as microchannel plates. All this results in a very sensitive instrument, with high mass resolution and capable of covering a wide mass range (from 1 to more than 10,000 mass units). But when the number of ions created is too high in the ionized volume, this affects the local electric field (extraction field) by space charge effect and this results in a loss of mass resolution of the instrument because the extraction of ions is strongly disturbed. Presented work : In this study, Comsol software (V 6.2) is used with the AC/DC module for electric field calculation (3D) and the Particle Tracing Module for space charge analysis and ions trajectory mapping in time and space. The limitation of mass resolution in relation to the space charge will be studied and quantified. Some ways to mitigate this effect will be analyzed using Comsol software.