Chromatography has found an increasingly wide utilization in scientific and technological fields, even in some cases, has become indispensable methods for analysis and separation. Compared with its application, some common queries in chromatography still lack for good theoretical explanations, for instance, the action of flow rate of mobile phase on symmetry of peak. As is familiar to people, an increase in flow rate of mobile phase always causes theoretical plate number to decrease under normal conditions. At the same time, maybe the symmetry of chromatographic peak obviously increases, on the contrary. This result is self-contradictory. Why does the theoretical plate number not increase under the condition? Utilizing our prior paper on five plate numbers in chromatography, this paper points out why theoretical plate number decreases with an increase in symmetry of peak when flow rate of mobile phase increases. Based upon gas-solid chromatography results, the relation between flow rate of mobile phase and frequency of partition of solute, and the relation between flow rate and plate number are deduced. From the angle of theoretical model, this paper discusses the relation between solute partition in static mobile phase such as partition between two phases in plate theory and solute partition in flowing mobile phase such as Martin-Synge partition in slip mechanism, and their characteristics.