The dramatic increase in waste plastics has created a hazard to our health and ecosystems. And separation of waste plastics has been the highlight of recycling because plastic mixtures make trouble for efficient reuse. Selective flotation attracts much attention due to its remarkable efficiency for separation of plastics with analogous physic-chemical characteristics. In this review, we specify the benefit of separation on plastic recycling, clarify the separation methods in plastic recycling and inspect the factors, methods, mechanisms and hindrances related to plastic flotation. Surface modification is emphasized as essential procedure for technical improvement of plastic separation. We propose practical schemes to improve the recycling of unavoidable fine particle and further try to eliminate the adverse impact from flotation on next procedure. It is predictable that landfill plastics and microplastics can be subjected to flotation separation to generate supplementary resource.