Abstract: The effects of glutamine transaminase (TGase), hydroxypropyl distarch phosphate (HDP), gellan gum and their complex (THG) on the water distribution and protein conformation of low-salt tilapia surimi gel prepared with microwave and ultrasound were analyzed. In addition, the effects of different exogenous substances on the characteristics of low-salt tilapia fish cake were explored through in vitro digestion experiment. The results showed that compared with the control group, THG increased the bound water and immovable water of surimi to 98.71% and 14.75%, respectively, and significantly decreased the free water content (P<0.05). Moreover, THG promoted the transformation of α-helix to β-folding, β-turning and random curling structures. TGase and THG (0.4%) played important roles on gastric emptying rate, protein digestibility and protein hydrolysis degree of low-salt tilapia cake. THG significantly promoted protein decomposition into aggregates with smaller particle size (P<0.05). After the digestion of stomach and duodenum, color of the THG group products was more transparent and clear. And it could be observed by the laser confocal microscope that the red fluorescence highlights of the THG group were significantly reduced, indicating that proteins had been fully digested. Hence, compared with a single exogenous substance, THG not only promoted the binding of water molecules and proteins and induced the change of protein conformation, but also facilitated the exposure of hydrophobic protein groups and the interaction between proteins, and promoted the digestion and absorption of surimi products in the stomach and duodenum. This project provided a theoretical reference for the research on the gel properties of tilapia surimi and the development and application of tilapia fish cake.