Composite construction is now the material of choice for sonar domes on surface ships and submarines. The domes provide a smooth flow around sonar transducers and protect them from impact damage. Protective dome of underwater sonar devices should comply with specific requirements with respect to acoustic behavior and protection. That’s why conventional steel crusts are being replaced by composites in the sonar industry in many developed countries as well as in Iran. Investigation of material properties indicated that good sonar transmission at various frequencies was achievable with composite material. When this attribute is coupled with weight-saving, freedom from maintenance and corrosion, and ease of fabrication of complex shapes. In this research the flow of resin and the parameters which affect it during vacuum assisted resin injection molding are analyzed. This is the process selected for the production of the composite protective structure. This process is commonly used in the production of large-sized high-quality composite items in small numbers. It involves a stiff mould half and a flexible membrane that seals the cavity. Vacuum is used to consolidate the preform, and atmospheric pressure drives low viscosity resin into the mould cavity. The part is cured at room temperature. A high permeability medium is added to the preform, in order to reduce infusion time. This material modifies flow dynamics during preform infusion. Proper filling of the mold and soaking of the fibers are critical in vacuum assisted resin injection molding. Inadequate soaking can result in faulty items and higher costs. Because of their common inability to properly model the process, manufacturers mostly prefer to use traditional manual methods. These methods, however, involve the use of larger amounts of resin which in turn results in higher evaporation and pollution and lower quality and durability of the final product. Simulation of the flow of resin can be a good way for ascertaining the proper filling of molds before the resin is congealed. Hence we studied the process and the equations and parameters involved in the modeling of the flow of resin. To conduct this study, we measured permeability and porosity of three types of glass fiber tissue and the way these parameters changed with pressure. The results were fed to a computer program for analysis. During the VARTM process, the flow front velocity changes imply that impregnated preform thickness, the porosity and the permeability values of the wet area varies with pressure gradient. The preform porosity decreased as the pressure increased and was affected by compaction of the preform locally with the pressure gradient. Preform permeability changed due to the compaction and flow pressure. It was increased as the compaction pressure increased and decreased as the Flow pressure increased. The largest effect of compaction pressure on permeability and in general the preform permeability decreased as the compaction and flow pressure were increased. Simulation was done using Fluent software (Ansys) and the results were compared to experimental ones so that their validity could be established. Simulated process times show 10% to 20% error which is probably due to error in the measurement of parameters, thickness changes during simulation not being accounted for, and general software error. The optimal strategy for resin injection was eventually determined through trial and error. Key words Modeling, Resin Injection, VARTM, Composite, sonar dome