The present invention relates to an electropolymerization method for preparing a nanotube-type conducting polymer using a porous template, a method for preparing an electrochromic device using electrochromism of the conducting polymer, and an electrochromic device prepared therefrom, and more particularly to an electropolymerization method for preparing a nanotube-type conducting polymer using a porous template to prepare an electrochromic device having good electrochromism by injecting an electrolyte solution wherein a precursor of the electrochromic conducting polymer is dissolved into an electrochemical reaction cell comprising a first transparent electrode and a working electrode, which is a porous template on the electrode, a method for preparing an electrochromic device using electrochromism of the conducting polymer, and an electrochromic device prepared therefrom.