The invention discloses a bismuth tungstate composite photocatalyst modified by a nitrogen-doped carbon quantum dot and a preparation method and application thereof. The composite photocatalyst is characterized in that bismuth tungstate is taken as a carrier, and is modified with the nitrogen-doped carbon quantum dot. The preparation method comprises the following steps: mixing bismuth nitrate, sodium tungstate and water, and stirring the mixture to obtain a bismuth tungstate precursor solution; mixing the bismuth tungstate precursor solution with a nitrogen-doped carbon quantum dot solution, and stirring the mixture to obtain a mixed solution; performing a hydrothermal reaction to obtain the bismuth tungstate composite photocatalyst. The composite photocatalyst has the advantages of environmental friendliness, high photo-induced electron-hole separating efficiency, high light absorbing efficiency, high photocatalysis activity, high photocatalysis stability and high corrosion resistance; the preparation method has the advantages of simple preparation process, low raw material cost, and easiness in controlling operation conditions. The composite photocatalyst is used for catalyzing degradation of antibiotic wastewater, and has the advantages of simple application method, high degrading efficiency and high repeatability, and has a very good practical application prospect.