The invention provides a method for improving heterotrophic microbial fermentation via multiple chemical promoters to produce docosahexenoic acid (DHA). The method comprises the following steps: with a heterotrophic culture medium of crypthecodinium cohnii as a foundation, adding any chemical promoter into the heterotrophic culture medium; the heterotrophic culture medium is composed of 9g/L of glucose, 2g/L of yeast extract powder and 25g/L of sea salt; the chemical promoter can also be called a plant growth regulator, including indoleacetic acid (IAA), naphthoxyessigsaeure (BNOA), chlorobenzoic acid, salicylic acid (SA), abscisic acid (ABA) and cholamine, and the concentrations of these chemical promoters in the heterotrophic culture medium are as follows: 2.5mg/L of indoleacetic acid (IAA), 4mg/L of naphthoxyessigsaeure (BNOA), 4mg/L of chlorobenzoic acid, 1mg/L of salicylic acid (SA), 20mg/L of abscisic acid (ABA) and 2.5mM cholamine; culturing at 25 DEG C for 72 hours, extracting grease, and measuring the DHA content of the culture by using a gas chromatograph-mass spectrometer, meanwhile, extracting cellular metabolite from a parallel culture, and detecting and analyzing the content change condition of the cellular metabolite by using a metabonomics method.