Abstract: The implementation of a 2D parallel particle-in-cell (PIC) simulation with domain partition is presented.Its performance is tested on a PC cluster of 16 Pentium Ⅲ 1.6 CPUs. It shows that the parallel efficiency decreases with the increasing of computation nodes while keeping the calculation size; and the parallel efficiency increases with the size of physical problem while keeping the number of computational nodes. It means that parallel computing is suitable for large physical problems. As an example, a calculation on plasma beam instability is performed with this parallel PIC code. The results show that in the linear growth stage, the excited Alfven waves propagate in the direction of ambient magnetic field, and they satisfy a resonant condition ω-kV_b=-Ω_i, where ω and k are frequency and wave number of the excited Alfven waves, respectively, V_b the beam velocity and Ω_i the ion cyclotron frequency.