The present disclosure relates to a method of counting step-number. When detecting step-number executed by an electronic device, a g-sensor of the electronic device detects whether the moving speed is normal (one step per second), i.e. the detection result is the G value, or the movement speed has abnormal variation (such as one step per two seconds or five seconds), i.e. the detection result is the G value at Y axis, and the electronic device computes the step-number according to sums of maximum values and minimum values of speed variations every second within a counting period, and average of the sums. The processing unit determines the variation of the step-numbers of the G values and the G values at Y axis, and selects one of the two step-numbers for use as a correct step-number detection result, so as to achieve the objective of precisely computing step-number upon the speed variation.