The invention discloses a multi-core composite carbon source for strengthening nitrogen removal during sewage treatment. A preparation method of the multi-core composite carbon source includes: addingstarch into hot water of 70-100 DEG C, and stirring to enable starch liquid to be fully gelatinized; adding a starch hydrolysis catalyst and acetic acid while stirring, hydrolyzing at 80-100 DEG C for 1-2h, and adding alkali until pH value of a solution is 5.5-7.0; adding microbial prebiotic factor, vitamin and mineral, stirring well, filtering, and decoloring to obtain the multi-core composite carbon source. The multi-core composite carbon source is rich in various carbon sources needed by different microbial flora for metabolism, and weakening of flora diversifying in environment with a single carbon source is avoided; the multi-core composite carbon source is rich in microbial prebiotic factors like various trace elements, organic acid and natural biological hormone, so that microbialactivity of a biochemical system is improved while carbon source supplement is realized, flora diversity is enhanced, and a carbon source which is more efficient is provided for denitrification.