<p>Although Kashin-Beck disease (KBD) in China has been effectively controlled through comprehensive measures such as selenium supplementation and grain replacement, the underlying environmental risk factors may still persist. There remains a potential risk of disease resurgence if prevention and control efforts are relaxed. To dynamically assess the selenium exposure levels in humans (using children’s hair selenium as a biomarker) and the selenium status in the external environment (soil selenium and grain selenium) in historical severe endemic areas and adjacent non-endemic areas in China, while simultaneously monitoring T-2 toxin contamination in grains, this study was conducted in six provinces/autonomous regions: Jilin, Heilongjiang, Shaanxi, Qinghai, Sichuan, and Tibet. Selenium levels in children’s hair (<i>n</i> = 2,276), staple grains (<i>n</i> = 2,130), and soil (<i>n</i> = 788) were determined using the 2,3-diaminonaphthalene fluorometric method, and T-2 toxin in grains was detected by enzyme-linked immunosorbent assay. The results showed that the average soil selenium content in both endemic and non-endemic villages across the six provinces was below 0.2&#xa0;mg/kg. Notably, soil selenium levels in endemic villages of Tibet and Shaanxi were slightly higher than those in non-endemic villages, suggesting that total selenium content alone is insufficient for predicting disease risk and that selenium bioavailability or other synergistic/antagonistic factors may be involved. The overall selenium status in children was at a moderate level; however, hair selenium levels in endemic villages of Sichuan were significantly lower than those in non-endemic villages. With the exception of Shaanxi, hair selenium levels in children from both endemic and non-endemic villages in the other five provinces exceeded 0.2&#xa0;mg/kg. Regarding staple grains, selenium levels were slightly above the critical value of 0.02&#xa0;mg/kg only in endemic and non-endemic villages of Sichuan and in endemic villages of Tibet; levels in all other surveyed areas fell below this threshold. Particularly in Tibet and Sichuan, grain selenium levels remain critically low, providing direct evidence for precisely allocating limited intervention resources to these “high-risk areas” and conducting long-term effect evaluations. T-2 toxin was detected in a minority of grain samples, and all detected levels were below the national safety limit (100&#xa0;µg/kg), indicating that the etiological combination for KBD still exists in the natural environment, albeit at exposure levels currently below the pathogenic threshold. Under the current circumstances, targeted interventions must not be relaxed. Selenium deficiency remains a more dominant risk factor than T-2 toxin exposure, and prevention strategies should focus more on sustained selenium nutrition interventions.</p>