Abstract: Elucidating the residue characteristics of thiamethoxam and its metabolite in melon and quantifying their diversified dietary risks to different populations in China are essential for safeguarding human health and agro-ecosystem safety. A rapid and trace analytical method for detecting thiamethoxam and its metabolite clothianidin in melons was developed using ultra-high performance liquid chromatography-triple quadrupole tandem mass spectrometry (UHPLC-MS/MS), and the stable stability of target pesticides was clarified. The diversification of multi-dimensional exposure risk was explored based on the parameters and dietary structure of Chinese populations. A large-scale field trials of pesticide was conducted and the results elucidated that the original deposition of thiamethoxam in melons ranged from 0.025 to 0.031 mg/kg, the degradation half-lives (t_1/2) lasted from 0.77 to 1.2 d, and the final residue level was ≤0.021 mg/kg. Additionally, 6.1% to 15% of thiamethoxam was metabolized to clothianidin during the growth period. The joint multi-registered crop assessment showed that the long-term risks of thiamethoxam and clothianidin in vegetable crops were significantly higher than those in fruits, cereals, soybeans, spices, potatoes, oilseeds, and sugar crops, of which rural areas were significantly higher than urban areas (p < 0.05). Deterministic modeling quantified the short and long-term dietary risks for thiamethoxam in melon as 0.043%-0.12% and 0.0078%-0.055%, and those for clothianidin were 0.0051%-0.014% and 0.00022%-0.0015%, respectively. The short and long-term risks of thiamethoxam and clothianidin fitted by probabilistic modeling were less than 100% at different percentiles, and the long-term risks at the 30^th percentile were closest to the deterministic results, and the short-term risks at the 60^th (thiamethoxam) and 90^th (clothianidin) percentile were closest to the deterministic results. Whether assessed as point or interval estimates, the dietary risk of thiamethoxam and its metabolite clothianidin for Chinese residents are acceptable, however, attention should be paid to the amplification of risk from diversified dietary exposure throughout the life cycle, especially for the susceptible pediatric populations.