Saltation is one of the important transport modes in the movement of wind-blown grains. Its evolution was considered to be a wind-particle self-regulating process. Recent researches indicate that the particle mid-air collision greatly influences the sand movement, thus the mid-air collision mechanism may highly contribute to the evolution of wind-sand flow. A theoretical model is suggested to mathematically describe the evolution of wind-sand flow by considering the exiting wind-particle feedback mechanism as well as the particle mid-air collision mechanism. Based on this model, the time of the entire process to reach a steady state, the variation curves of the sand transport rate with time and the mid-air collision probability with time are calculated. The results show that the mid-air collision mechanism also contributes significantly to the stabilization of the saltation process.