A privacy filter and its preparation method are disclosed. One embodiment of the privacy filter comprises: a first transparent substrate; a second transparent substrate positioned a predetermined distance apart from and opposite to the first transparent substrate; an electrolyte filled between the first and second transparent substrates; and a second transparent conductive layer disposed between the electrolyte and the second transparent substrate. The first transparent substrate comprises: an uneven pattern having a wire grid and trenches formed on the first transparent substrate; a first transparent conductive layer formed on the wire grid and the trenches of the uneven pattern; and an electrochromic layer being formed on the first transparent conductive layer along the sidewall of the wire grid and containing an electrochromic material to transmit or absorb visible light depending on whether an electrical signal is applied or not.