The invention relates to an oxygen doped porous carbon nitride visible light catalytic material and a preparation method thereof, and belongs to the technical field of material preparation and photocatalysis. Nitrogen-rich compound urea is used as a precursor; AO (ammonium oxalate) is used as an oxygen source and a foam template agent; a direct thermal polymerization method is used for preparing oxygen doped porous carbon nitride. The AO is decomposed into NH3 and CO2 at high temperature to promote the formation of the porous structure in the urea thermal polymerization process; oxygen atoms are successfully introduced into carbon nitride; the absorption on visible light can be effectively promoted; further, the photocatalytic performance is improved. The method has the advantages that theproduction process is simple; the repeatability is high; the cost is low; the green and environment-friendly effects are achieved; good application prospects are realized in the field of photochemical catalysis.