P53 pulses refer to the fluctuation of the p53 protein levels in the cells in a periodic or repetitive manner. The mechanisms for triggering P53 pulses lie in several kinds of the positive and negative feedback loops in the p53 network. Two core feedback loops include the p53-Mdm2 negative feedback loop and Wip1-ATM-p53 negative feedback loop. Owing to the existence of these feedback loops, a limit cycle and a given number of P53 pulses were generated when the p53 system entered the limit cycle region. Pro-apoptotic regulator and P53 existing in different form are gradually accumulated as the number of P53 pulses increases and then the irreversible cell fate is determined by opening apoptotic "switch" above the threshold level. The cell fate can be determined by the number of P53 pulses partly, but it also has close relationship with its frequency, amplitude and wave form. Therefore, it is of great significance for the mechanism investigation of diseases development, prevention and treatment.