The factors affecting the water activity of semi-dried salted fish were studied by adding quality improver and controlling the salt content of the final product, and the effects of quality improver on the water activity of semi-dried salted fish were discussed. The results showed that the water activity of semi-dried salted fish products mainly depended on the salt content of the final products, and the water activity decreased significantly with the increase of salt content; Propylene glycol, glycerol, sodium dihydrogen phosphate and disodium hydrogen phosphate can also significantly reduce the water activity of semi-dried salted fish by adding proper amount of quality improvers such as propylene glycol, glycerol, sodium dihydrogen phosphate and disodium hydrogen phosphate