Abstract: To address the issues of shrinkage cracking, high energy consumption and high carbon emission of traditional cement-based sealing materials, the authors investigated the use of sodium alginate (SA) crosslinking metal ions to prepare SA modified alkali activated waste incineration base ash (MSWI-BA) -granulation blast furnace slag (GBFS) based gaging plugging material (SWM). The optimal water-solid ratio was determined by evaluating compressive strength and setting time to be 0.4. The influence of SA modification on the high temperature resistance of the gelling material was investigated by analyzing the compressive strength, shrinkage rate, and fracture morphology of the gelling material at different temperatures. The results showed that after SA modification, the high temperature resistance improved, the surface cracks on the modified cementable material were significantly reduced after heating, and the shrinkage rate was reduced by 26.5% compared to that before modification. The residual compressive strength is still as high as 17.25 MPa after heating at 400 ℃. Combined with microscopic morphology, pore structure properties, and thermal analysis experiments, the generation mechanism of SA modified gelling material was examined. The results revealed that the SA modified MSWI-BA-GBFS based gelling material refines pore size and reduces pore volume via coordination crosslinking of SA and Ca²⁺/Al³⁺ and the synergistic effect of the silico-aluminate covalent network, thus maintaining the matrix structure's integrity after heating, improving cracking properties. The simulation findings suggest that the leakage plugging performance of SA modified MSWI-BA-GBFS based gelling material with water solid ratio 0.4 is superior to that of mining cement-based material, demonstrating a better leakage plugging performance. The development of SA modified MSWI-BA-GBFS based gelling plugging material not only provides an effective way for the resource utilization of municipal waste incineration bottom ash, but also provides a type of environmental protection fire-fighting material with high compressive strength, anti-shrinkage cracking, and high temperature resistance, which can completely replace the traditional mine cement based plugging material.