1. An input method for being loaded into a processor to execute following steps: triggering an input device to perform a gesture input process, comprising: recording a triggered site of a gesture as a sampling point once every unit of time, and recording a turn variation of an interval link between one said sampling point and a next said sampling point; comparing the turn variation to a variation threshold, and when the turn variation is greater than the variation threshold, marking the relevant sampling points as a featured sampling point; chronologically linking plural said featured sampling points into featured line segments, recording proportions of lengths of the featured line segments, and forming a graphic code according to the proportions; and comparing the graphic code to codes contained in a lookup table, so as to perform a predefined function represented by the graphic code.