Electromagnetic-wave propagation through equilibrium plasmas can lead to medium instabilities whose formation and growth conditions are of importance to study. Raman forward scattering (RFS) instability in low-density plasmas is investigated through particle-in-cell (PIC) simulation, which is employed due to plasmasâ high complexity, costly experiment process, and nonlinear behavior in physical terms. A 2D electromagnetic PIC code is used to model RFS instability. Doing so, a plasma medium containing ions and electrons is PIC simulated and ions are assumed to form a constant background because of high inertia. The results indicate that as a plane electromagnetic wave enters the plasma medium, large-amplitude longitudinal waves, whose growth rate is well consistent with the theoretical results, begin to grow, suggesting the appearance of RFS instability.