An input apparatus using multidimensional electrodes to define key functions and the encoding method thereof is peculiarized by utilizing N-dimensional electrodes to define the individual key functions, where N is a positive integer number greater than two. The keyboard scan process according to the present invention is to perform the scan on the coordinate electrodes one by one and save the scan codes for making a synthetic determination, so as to identify the key being pressed. The keyboard encoder IC using the keyboard scan process of the present invention is advantageous to the pin number reduction and cost descent.