Study on Dictyostelium discoideum cell cycle can provide theoretical foundation for research of the eukaryotic cell cycle regulation. In this study, the cell counting and cell doubling time calculation indicated that the allC mutant doubling time was 2.36 h, only one third of that of KAx-3 cells. To search for the reason of shortened allC mutant doubling time, the function of cyclin B1, cell cycle of mutant cells and wild cells were studied by flow cytometry and real time-quantitative PCR. After cultured for 16 hours, the number of the mutant allC cells (1.51%) in the G2 phase was significantly less than that of KAx-3 cells (16.61%)(P<0.05). The relative expression level of cyclin B1 in allC mutant and KAx-3 cells were 2.5 and 0.24, respectively. It has demonstrated that the G2 phase of allC mutant was obviously shorter than that of KAx-3 cells, so was the relative expression level of cyclin B1 which was related closely to G2 phase regulation. Our results suggest that the overexpression of cyclin B1 in allC mutant may affect the normal cell cycle regulation to some extent, and it contributes to G2 phase abnormality.