<p>The stability of the canal embankment in the Middle Route of the South-to-North Water Diversion Project is crucial to the project’s safety. However, the expansive soil widely distributed along the route tends to damage the canal embankment, owing to its strong swelling and shrinkage properties. Moreover, termite nests resulting from frequent termite activity in the region disrupt the continuity of the soil mass and exacerbate the deterioration of the expansive soil’s tensile strength, thereby posing a dual threat. Therefore, investigating the tensile strength characteristics of expansive soil in environments containing termite nests is highly relevant for engineering applications. Splitting tests were conducted on expansive soil containing termite nest pores using Particle Image Velocimetry (PIV). The test results revealed the following: The tensile strength of expansive soil decreases as the pore diameter of the termite nest increases. This is mainly because the termite nest pores reduce the effective bearing area, intensify stress concentration, and induce rapid crack propagation. The tensile strength decreases as the water content increases. The primary reason is that decreasing matric suction causes expansive soil to absorb water and swell, increases the void ratio, and substantially weakens interparticle cohesion. Based on the test results, a prediction model for the tensile strength deterioration of expansive soil was established. The findings of this study provide a scientific basis for evaluating the tensile strength of expansive soil containing termite nests, and offer important practical guidance for the later-stage, high-quality development of the Middle Route of the South-to-North Water Diversion Project.</p>