•Low salt affects the nutrient composition of Eriocheir sinensis.•The increase of free amino acid content is related to organism metabolism.•The change of free nucleotide is related to the degradation pathway of ATP.•Lipid accumulation during development affects fatty acid composition. In this paper, the effects of temporary rearing time on the flavor substances of the edible parts of river crabs under the condition of 7 psu were determined based on high performance liquid chromatography (HPLC) and gas chromatograph (GC) techniques. The results showed that the content of free amino acids in the edible parts of river crabs could be increased under the condition of salinity of 7 psu. The content of organic acids in the edible part of Chinese mitten crabs was also affected by temporary culture under salinity 7 psu, and the change trend was the same as that of amino acids. The treatment of 7 psu can promote the accumulation of free nucleotides in the muscles, hepatopancreas and gonads of the crabs, and the equivalent umami concentration (EUC) values in the muscles and gonads of the crabs have been significantly increased. However, salinity 7 reduced the proportion of PUFA in muscles and gonads, resulting in a certain amount of nutrient loss. In summary, 15 days after treatment with salinity 7 can significantly improve the flavor of the edible parts of Chinese mitten crabs.