A novel barrier screw scientifically designed with new structural features that eliminate the shortcomings of the previous barrier screws and further improve their performance. The important new structural features include a structure of originating the barrier flight without creating any dead-spot while maintaining a constant solid channel width, a structure of terminating the barrier flight without creating any dead-spot while assuring good melt quality, a melt channel structure of avoiding excessively deep channel depth while assuring sufficient melt conveying capacity, and a solid channel structure of avoiding excessively large channel area with shallow channel depth while assuring good melt quality.