The present disclosure provides a method and a system for obtaining a cycle of a physiological signal. The method includes: receiving a physiological signal value and a register value, comparing the physiological signal value with the register value, and reserving one of the physiological signal value and the register value determining the physiological signal value with a time duration thereof reaching a given set time to be an extreme value and restarting the procedure and determining a next extreme value and obtaining a cycle of the physiological signal by calculating a time difference between the extreme value and the next extreme value. In the present disclosure, the cycle of the physiological signal can be obtained by the extreme value recognition algorithm, which is simple, fast, of high efficiency, and of high reliability.
