Acyl carrier protein ( ) is an acyl carrier in fatty acid synthesis and is an important cofactor of fatty acid synthetase. Little is known about ACP in insects and how this protein may modulate the composition and storage of fatty acids. We used an RNAi-assisted strategy to study the potential function of ACP in (Diptera: Stratiomyidae). We identified a gene with a cDNA length of 501 bp and a classical conserved region of DSLD. This gene was highly expressed in the egg and late larval instars and was most abundant in the midgut and fat bodies of larvae. Injection of significantly inhibited the expression level of and further regulated the fatty acid synthesis in treated larvae. The composition of saturated fatty acids was reduced, and the percentage of unsaturated fatty acids ( ) was increased. After interfering with , the cumulative mortality of increased to 68.00% ( < 0.05). growth was greatly influenced. The development duration increased to 5.5 days, the average final body weights of larvae and pupae were decreased by 44.85 mg and 14.59 mg, respectively, and the average body lengths of larvae and pupae were significantly shortened by 3.09 mm and 3.82 mm, respectively. The adult eclosion rate and the oviposition of adult females were also severely influenced. These results demonstrated that regulates fatty acid content and influences multiple biological processes of .