1. A smoothing method for time data sequences, the method is executed by a hardware processor to perform: smoothing a plurality of original data points of a time data sequence, then from a plurality of smoothed data points, determining a plurality of reference points for a current global-trajectory trend and a current local-trajectory trend; calculating a global trajectory direction and a local trajectory direction of the time data sequence; according to the plurality of reference points; and adaptively calculating at least one new data point by integrating the global trajectory direction and the local trajectory direction.