Objective: To explore the difference between PI and 7-AAD nucleic acid dyes on the detection of cell cycle experiments and the effect of RNase with the staining of the two dyes by flow cytometer. Method: Using ModFit LT 4.1.7 software analyse cell cycle data and assess the effects of the two different dyes and RNase on cell cycle results. Coloring of cell lines HCCLM3, HepG2 and HEK293T by PI or 7-AAD, with or without RNA digestion, respectively. Results: Only the colouring of the PI cell cycle has a significant effect on by RNase, but the 7-AAD cell cycle does not. For RNase-treated samples, PI staining to detect the cell cycle is more precise than 7-AAD staining to detect the cell cycle.