To investigate the changes of flavor components of Oreochromis niloticus during the processing of Shanghai smoked fish, high performance liquid chromatography (HPLC), amino acid auto-analyzer and gas chromatography-mass spectrometry (GC-MS) were employed to analyze and identify the flavor components of Shanghai smoked fish in four processing stages (fresh O. niloticus, the first pickling, the first pickling followed by frying and Shanghai smoked fish products). The results showed that IMP, as main umami nucleotide, its contents of later stages were significantly higher than that of the earlier stages. Moreover, the contents of free amino acids and taste amino acids had the same trend as the IMP, among them, aspartic acid and glutamic acid had the greatest influence on the flavor of Shanghai smoked fish. In addition, 50, 84, 78 and 82 volatile components were detected in fresh O. niloticus, first pickling, first pickling followed by frying and Shanghai smoked fish products respectively, which were mainly composed of aldehydes, ketones, alcohols and hydrocarbons. Therefore, its fishy smell of O. niloticus was greatly improved by pickling and frying as they were the main cause of its flavor formation.