Flow regimes in a gas-solid cylindrical fluidized bed of 150mm (i.d.)x1.2m (high) with three different sand masses (1.5, 3, and 4.5kg) were studied via information entropy analysis of pressure fluctuations. Three classes of methods of information entropy were adopted to characterize the flow regimes. It is shown that the first-class dimensional methods are suitable for illustrating the distinct characteristic of the flow regimes under different operating conditions, while the other two dimensionless methods are appropriate for finding the similarities or common rules. Tsallis entropy and Renyi entropy do not provide more valuable information than Shannon entropy. Most importantly, the Shannon entropy method is a good choice for characterizing the flow regimes but is weak at revealing the transition velocity (U-c) clearly. This deficiency can be made up by the method of component Shannon entropy. Shannon entropy is partitioned into 4 component Shannon entropies (named CH1CH4), which may be related with a 4-stage fluidization process assumption. A rule is found that the transition of flow regimes transition from bubbling bed to turbulent bed takes place when the contribution proportion of CH3 is exceeded by that of CH1, and it brings new enlightenment on interpretation of the transition mechanism.