The invention discloses a modified graphite phase carbon nitride photocatalyst as well as a preparation method and application thereof. The modified graphite phase carbon nitride photocatalyst is prepared from urea and salicylic acid serving as raw materials by virtue of calcination, wherein a mass ratio of urea to salicylic acid is 1:(0.002-0.02). The modified graphite phase carbon nitride photocatalyst disclosed by the invention has the advantages of being high in specific surface area, wide in light absorption range, low in electron-hole pair recombination rate, excellent in photocatalyticperformance and the like, and has multiple reactive sites, excellent application value and application prospects. The preparation method has the advantages of being simple in process, wide in raw material source, low in cost, high in preparation efficiency, high in yield and the like, is suitable for large-scale preparation and is favorable for industrial production. The modified graphite phase carbon nitride photocatalyst disclosed by the invention can be used for degrading organic pollutants, has the advantages of being simple in process, convenient to operate, low in cost, high in treatmentefficiency, excellent in degradation effect and the like, and has excellent effects of degrading the various organic pollutants.