Abstract: In order to effectively condition and loosen tobacco bales and decrease steam consumption, a composite vacuum pre-conditioner was designed by incorporating rotary vacuum conditioning and loosening technologies. The pre-conditioner was mainly composed of a driving device for vacuum conditioning, a rotary sealing device, a conditioning device and a cylinder body with tobacco buildup prevention structure. Five testing batches of tobacco bales were processed by the designed pre-conditioner under different technical conditions, the results showed that: 1) The ordering efficiency of tobacco strips reached 100%, their loosening rate was up to 98% with a uniform moisture content. 2) The technical parameters of the new pre-conditioner were adjustable over a wide range, allowed it to process tobacco bales at different intensities; the temperature of the processed tobacco was 50 ℃ or 65 ℃. 3) No tobacco built up on the inside wall of cylinder basically, it was convenient in maintenance. 4) The steam consumption reduced by 35% comparing with a traditional vacuum pre-conditioner. Rotary vacuum conditioning system provides an alternative for the vacuum conditioning of tobacco.