Cut tobacco size distribution (CTSD) is a key factor influencing cigarette physical quality. In this paper, a batch of cut tobacco was passed through a Protos maker for six times to generate six different CTSD. The relationship between CTSD and cigarette physical quality was established by grey incidence. The results showed that: 1) There existed a critical size value. Those portions, which were above the size value, affected the physical quality of cigarette positively, while those portions below the value affected negatively. In the said test conditions, the size value was 2.80mm. 2) There existed a maximum incidence coefficient between cut tobacco size and cigarette physical quality. The closer to this marginal size, the greater the incidence coefficient. The marginal size was different for different cigarette physical quality parameters. In the said test conditions, it was 2.80mm for individual cigarette weight, tobacco rod density and draw resistance, 0.71mm and 1.00mm for the ends fallout and loose ends respectively. 3) The effects of CTSD on individual cigarette weight, tobacco rod density draw resistance, the standard deviation of draw resistance, ends fallout and loose ends were contrary to its effects on the standard deviation of individual cigarette weight, tobacco rod density and hardness, however, the ends fallout and loose ends was more affected by shorter strands, therefore, to manufacture a cigarette of good physical quality demands the majority of cut tobacco to fall in a given size range and minimize the proportion of shorter strands. In the said test conditions, the most probable size of the cut tobacco was considered to fall in the range of 2.00~4.75mm.