Particle-in-cell/Monte Carlo collision (PIC/MCC) algorithms are an outstanding numerical method for predicting the kinetic characteristics of discharge plasma. However, heavy computational costs limit its application, especially in large-scale plasma simulations. To investigate the distribution properties of plasma in magnetoplasmadynamic (MPD) thrusters, we used a scale reduction method called scaling law to simplify and accelerate the PIC/ MCC simulation. In this method, the physical processes, including the particle motion and collisions, of discharge plasma remained unchanged, thereby preserving the similarity of the discharge system before and after scaling. On the basis of the scaling law, all the scaling schemes of the relevant physical quantities were obtained. We verified the scaling law by analysing the electron trajectories and densities in electromagnetic fields at different scaling factors. The scaling methodology shows great advantages in reducing the total computation and the time to achieve the convergence of the simulation. Therefore, the PIC/MCC model with the scaling law provides an efficient and in-depth understanding of the discharge plasma in MPD thrusters.