The invention relates to the field of semiconductor materials, and aims to provide a C3N4 nanowire photocatalyst and a preparation method thereof. The preparation method comprises the following steps: calcinating a nitrogen-enriched precursor at high temperature, then adding an alkaline solution, filtering, washing with water and drying to obtain the C3N4 nanowire photocatalyst. The C3N4 nanowire photocatalyst has good photocatalytic performance, is simple in preparation process, short in reaction time, environmentally friendly in technology and high in repeatability, and is easily produced industrially.