Abstract: To effectively improve the quality of surimi gel, a soybean protein isolate-tea polyphenol (SPI-TP) complex emulsion was developed using SPI as the emulsifier and TP as the antioxidant. The effects of this emulsion on quality-related indicators of Spanish mackerel surimi gel, including texture, water-holding capacity, color, and flavor, were investigated. In addition, changes in the molecular conformation of myofibrillar proteins were analyzed to clarify the underlying mechanisms. The results showed that replacing soybean oil (5 g/100 g surimi) with SPI-TP complex emulsion (3% SPI concentration, 0.3% TP concentration, and 5% w/w emulsion addition level) markedly enhanced surimi gel properties. Specifically, hardness, gel strength, and water-holding capacity of the surimi gel in the SPI–TP group were 1075.88 g, 1010.70 g·mm, and 81.66%, respectively. Compared with the control group, these values increased by 37.45%, 60.48%, and 19.98%, respectively. Furthermore, cooking loss rate of the surimi decreased substantially, and texture parameters such as springiness and resilience were also effectively improved. Electronic tongue and electronic nose analyses revealed that the addition of the SPI-TP complex emulsion significantly enhanced umami taste of the surimi gel while reducing its fishy odor. Furthermore, microscopic and rheological analyses revealed that the microstructure of the group containing the SPI-TP complex emulsion was most compact and uniform, and both storage modulus and loss modulus of the gel were significantly increased. Multispectral analysis confirmed that the addition of the SPI-TP complex emulsion facilitated moderate unfolding of the myofibrillar proteins and induced a transformation of the protein secondary structure from α-helix to β-sheet, thereby strengthening intermolecular cross-linking interactions. Collectively, these findings demonstrate that replacing soybean oil with the SPI-TP complex emulsion markedly improves surimi gel properties by altering the conformation of myofibrillar proteins. The results of this study provide a theoretical basis for the application of complex emulsions in the development of high-quality surimi products.