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Poloxamer is a thermo-sensitive synthetic polymer that can achieve sol-gel transition with temperature change, but its relative molecular mass is low, and the hydrogel structure is difficult to maintain for a long time. The thermo-sensitive sodium alginate/poloxamer composite hydrogel (SA/P₄₀₇) was synthesized by mixing poloxamer with sodium alginate. The chemical structures, temperature sensitivity, microscopic morphology, dynamic viscoelasticity and <i>in vitro</i> drug release behaviors of sodium alginate/poloxamer composite hydrogels were investigated by FT-IR, test tube inversion, SEM, rheometer and UV-Vis spectroscopy. In addition, the swelling properties of sodium alginate/poloxamer composite hydrogels were also studied. These results show that the sodium alginate/poloxamer composite hydrogel is thermo-sensitive, and the gelation concentration (mass fraction is 6%) of poloxamer at body temperature can be reduced by adding sodium alginate. By controlling the mass ratio of sodium alginate and poloxamer, the sol-gel transition temperature can be kept between room temperature and body temperature (25-37 ℃), and the gelation time can be shortened to 84 s. The sodium alginate/poloxamer composite hydrogel has a structural feature of high porosity and interconnected pores, and its pore size ranges from 20 <i>μ</i>m to 80 <i>μ</i>m. With the increase of sodium alginate, the swelling rate of the sodium alginate/poloxamer composite hydrogel is gradually decreased. The sodium alginate/poloxamer composite hydrogel shows sustained release of the anticancer drug gemcitabine, and the drug release time can reach 72 hours. Sodium alginate/poloxamer composite hydrogel has an important application prospect in the field of injectable carriers for sustained drug release.