A signal filtering method for filtering signals obtained at a number of time points by an electronic device is provided. Each of the signals corresponds to an i-th value at an i-th time point of the abovementioned time points, and the i-th value and an (i+1)-th value are defined as an i-th ordering sequence, wherein i is a positive integer. Each of the i-th ordering sequence and an (i+1)-th ordering sequence conforms to a first strict monotonicity. The method includes the following steps. Firstly, whether an (i+2)-th ordering sequence conforms to a second strict monotonicity is determined. If yes, then execute the next step. Determine whether an (i+3)-th ordering sequence conforms to the second strict monotonicity. If not, a signal obtained at an (i+3)-th time point is deleted.