The disclosure discloses a pulse cycle detection device comprising: a sensor for sensing a pulse wave signal of a subject; and a processor for processing a digital pulse wave signal which is analog-to-digital converted from the pulse wave signal sensed by the sensor, to detect the pulse cycle of the subject. The processor is configured to perform operations of: calculating a differential value of the digital pulse wave signal over time; whenever a transition from positive to negative occurs to the differential value, determining that the pulse wave signal reaches a maximum point and recording the time value corresponding to the maximum point; once the differential value is less than a dynamic threshold, recognizing a last recorded maximum point as a peak point of the pulse wave signal; and calculating a difference between time values corresponding to two successive peak points for deriving the pulse cycle. Also disclosed are a pulse cycle detection method and a wearable electronic device. The pulse cycle detection device and method improve the timeliness and accuracy of the pulse cycle detection.