The invention discloses a new synthesis method for a BCL-2 inhibitor Venetoclax. The synthesis method includes the steps that 2,4-difluoro methyl benzoate serves as a raw material, the 2,4-difluoro methyl benzoate and 5-hydroxy-7-azaindole are subjected to a condensation reaction, Ven-16 is obtained, and 4-substituted isomer and other impurities are removed through recrystallization; the product and N-Boc-piperazine are reacted and hydrolyzed, and Ven-18 is obtained; Ven-18 and Ven-21 are condensed, Boc of trifluoroacetic acid is removed, and Ven-20 is obtained; the product and Ven-7 are reacted, reaction intermediates in all the steps have the good crystal forms, purification can be carried out through crystal to achieve the center control requirements of the technology, and a final product Venetoclax can also be subjected to recrystallization to obtain the product Venetoclax, wherein the HPLC purity of the Venetoclax is larger than 99.5%, and the individual impurity of the Venetoclax is smaller than 0.1%; the Venetoclax has the industrialized application value.