Abstract: To improve the separation efficiency of green leaf thresher, a pneumatic separator with heavier tobacco bypass was designed, meantime, the processing flow of the first stage pneumatic separating was modified accordingly. A mechanical roller is used to project tobacco, a deflector plate is used to adjust the projecting angle and distance, thereby to increase heavier tobacco output and deliver it directly to the second stage thresh, and to separate lighter tobacco from heavier tobacco precisely. The new separator was tested with tobacco of grade WCC3F in Tongren Redrying Factory of Guizhou Tobacco Redrying Limited Corporation, and the results showed that: 1) Compared with traditional pneumatic separator, the separation efficiency of the newly designed separator raised by 6.57 percentage points, the proportion of bypassed heavier tobacco reached 45%, the stem content in strips was less than 0.65%. 2)The moisture content and temperature of the heavier tobacco that went into the second stage thresher raised by 1.5 percentage points and 7.3 ℃ respectively, the large and medium-sized strip percentage increased by 0.69 percentage points, the breakage rate of strips was less than 0.25%, and the stem content in strips reduced by 0.23 percentage points. This technology provides a support for promoting the production performance of threshing lines.