Abstract: Packed tower and plate tower were common equipment in the operation of chemical units. The calculation of the height of the packing layer in the packed tower and the determination of the number of theoretical plates in the tray tower were the key. The calculation of the height of the packing layer in the textbook was based on the mass transfer unit, and the determination of the theoretical plate in the plate tower was determined by the McCable-Thiele method, and the relationship between the number of mass transfer units and the theoretical plate was less. In this paper, The mass transfer unit number and the theoretical plate number were respectively calculated by the absorption factor method in detail, and the quantitative relationship between them was established. It could be used for the comparison of the two type towers, which had a certain guiding role for the analysis and design of the tower, and helped students to learn and understand the process of absorption and rectification unit operations.