In this paper, we use polypropylene (PP) fibers (1.67dtex × 40mm) as a test material to prepare roving for measuring the drafting force in the break draft zone. We investigate the influence of the roller gauge, draft ratio, and roving twist factor on the drafting force to realize the drafting behavior during roller drafting of the PP roving. In actual spinning, we spin the 18.5 tex PP spun yarn to correlate the variation in drafting force and the yarn properties by evaluating the yarn quality index. The results show that we can obtain the best yarn quality under drafting conditions of 1.2-1.3 break draft ratio and 62 mm back roller gauge in conjunction with a roving of 0.476g/m and 7.7 twist factor.