Abstract: In order to quantitatively describe the retention of smoke components by residual tobacco rod during smoking, three approximate mathematical models for the filtration process were derived from different hypotheses of the retention process based on the filtration mechanism. The results showed that: 1) The expression of retention in the three mathematical models had a common double exponential form and could be unified into a general expression. 2) The double exponential expression could fit the retention data of smoke components by the tobacco rod and the filter satisfactorily. 3) According to the general expression, the model parameter conditions for selective filtration by the filter and the quantitative relationship between the selective retention coefficient and the model parameters could be derived. 4) The general retention rate expression could be used to explain the difference in retention efficiency by different sections of the same filter.