Abstract: For producing combined cavity filter rods, a disc-type filter unit positioning device was designed on the basis of KDF2 filter rod maker. The device consists of filter unit guides and three toothed transfer discs (including the first gap diminishing disc Ⅰ, the second gap diminishing disc Ⅱ and positioning disc) with the same tooth number and the same tooth width, which is consistent with the cavity length of the combined cavity filter rod. The tooth spaces of the disc Ⅰ is wide enough to receive the filter unit lengthwise from upstream reliably. To diminish the gap formed thereby between the tooth and the filter unit, the tooth space is decreased step by step through disc Ⅰ to the positioning disc, where the tooth space is exactly to the cavity length, it means the gap is diminished to zero, the filter unit is precisely positioned. In addition, by optimizing the diameter and rotational speed of the three rotary discs, stable transfer of the filter units can be achieved. The modified KDF2 filter rod maker was used to produce combined cavity filter rods of two specifications. The results showed that the maker could operate stably at a speed of 100 m/min. The proportion of filter units with phase deviation within the acceptable range was about 95%, the rate of missing or broken filter units was ≤0.6%, the frequency of rod blocking was ≤0.4 times per 10 000 rods, and the qualified rate of cavity length was over 99%. The designed device effectively meets the needs of combined cavity filter rod production.