The particle critical impact velocity is a key parameter in cold spraying. The appropriate estimation of this critical velocity benefits the optimization of coating deposition in terms of deposition efficiency. The critical velocity can be estimated experimentally through measuring the relation between deposition efficiency and particle velocity. A recent study has revealed that the critical velocity can be estimated by the velocity resulting in the onset of adiabatic shear instability through numerical simulation of particle impact. However, it was found that the critical velocities of a pure metal material obtained by different investigators through simulation were significantly different. No reasonable explanation was provided to such difference. In the present paper, the critical velocities reported in the literature for Cu powder as a typical material were reviewed. The factors influencing the critical velocity were examined. The numerical simulation methods employed in the limited literature were also examined for a better understanding of the factors that influence the simulated results. A reasonable estimation method was proposed by using the numerical critical velocity.