Abstract: In order to establish the precipitation mechanism when adding potassium citrate into tobacco concentrate to prepare the coating liquid used for paper-making reconstituted tobacco, the relationship between the precipitate content and the potassium citrate addition rate was investigated. The contents of anions and cations in the tobacco concentrate and the centrifugal supernatant of the coating liquid were measured by ion-exchange chromatography and the main ions participating in precipitation reaction were analyzed by calculating their lost rate during centrifugation. The results showed that:1) The precipitate content in the coating liquid increased with the increase of the addition rate of potassium citrate. 2) The main anions participating in the reaction were citrate, malate and oxalate, while the main cations were calcium and magnesium ions. 3) The shifting of acid-base equilibrium and precipitation-dissolution equilibrium were the intrinsic formation mechanisms of the precipitate.