Abstract: By integrating multi-source radioactivity survey data and using Geodetector, this study explored the spatial variations of the gamma radiation field at the ground-air interface and their influence mechanisms in the Pearl River Delta economic zone. The results indicate that key factors influencing the distribution of the radiation field include soil radon concentration (q=0.852), ²³⁸U content (q= 0.816), and ²³²Th content (q=0.803). Besides, formation lithology (q=0.791), fault structures (q=0.786), and chronostratigraphy (q =0.778) also play a significant role. The interaction detection indicates that the synergy of soil radon concentration and fault structures demonstrates the strongest explanatory power (q=0.875), suggesting the mechanism of structure-controlled transport and soil-controlled accumulation. Risk detection demonstrates that high-radiation radon contributors include normal faults, magmatic rocks, and Jurassic strata. The results of this study reveal that the spatial distribution of the radiation field is governed by a three-level system comprising nuclide content as a direct source, lithology and chronostratigraphy as carriers, and fault structures as pathways for radon transport.The research results have provided a scientific basis for regional radiation environmental risk assessment and pollution prevention and control.