In this paper, the characteristics of plastics particles in the cutting products and flotation behaviours of plastics were studied. On this basis, the relation of floatability of plastics with surface chemical related factor and gravity factors was derived and discussed. From the results, it was shown that plastics flotation is dominated not only by surface chemical factors, but also significantly by gravity factors. It is suggested that plastics flotation is a combination of froth flotation and gravity separation. According to this relation, the idea of particle control was first applied for the separation of plastics mixture. From the separation results, it can be seen that this method can greatly increase the separation efficiency for flotation separation of plastics mixture