The present invention provides a method for detecting bicycle pedaling frequencies, in which an accelerometer of the body is used to detect the acceleration value of the pedal during pedaling, and the processing unit determines the periodical variations on acceleration increases and decreases, records the acceleration waveform, calculates the number of cycling in the pedal per minute based on the times that the sampled values within a unit time cross over the central line of the acceleration value, and also transfers tempo data to an electronic device by way of a wireless communication circuit and displays the pedaling frequency of the pedal via a screen so as to allow a user to promptly appreciate relevant information during riding and facilitate appropriate adjustments and controls on pedaling tempo and force.