Fish gelatin (FG) is more suitable for consumption by religious people than mammalian gelatin. One common modification method of FG is mixing FG with polysaccharides. However, the mechanism is not clear. We found that FG gel containing 0.1 g/100 mL gellan, 20 mmol/L CaCl2 and 6.67 g/100 mL FG (180 Bloom) matched gel strength, hardness, cohesiveness, chewiness as well as gelling temperature (Tg) and melting temperature (Tm) of commercial beef gelatin (BG) (240 Bloom). The modified FG was also observed by the result of helix/coil ratio and spherical aggregates. The modification decreased the diameter of FG's aggregates from 472 to 249 nm, which matched with BG (272 nm, P < 0.05). Co-existence of segregative gellan-gellan fibrous aggregates and associated FG-gellan amorphous structure were also identified at the modified FG by atomic force microscope (AFM). The helix/coil ratio and diameter of spherical aggregates were inversely correlated, the mechanism behind was the strength of gelatin association. The involvement of hydrogen bond and presence of FG-gellan complex have been validated by urea addition and Fourier transform infrared (FTIR) spectroscopy. A schematic model was proposed. As modified FG successfully matched the of texture properties of BG, it is promising to replace BG with FG.