HO_x radicals (OH and HO₂) are crucial oxidants that determine atmospheric oxidation capacity and the production of secondary pollutants; however, their sources and sinks remain incompletely understood in certain rural, forest, and maritime environments. This study measured ${\mathrm{HO}}_{\mathrm{2}}^{\ast }$ (HO₂ + contribution from RO₂, organic peroxyl radicals) and OH concentrations using a chemical ionization mass spectrometer at a subtropical rural site in southern China from 12 November to 19 December 2022. The average peak concentrations were 3.50 ± 2.47 × 10⁶ cm⁻³ for OH and 1.34 ± 0.93 × 10⁸ cm⁻³ for ${\mathrm{HO}}_{\mathrm{2}}^{\ast }$. Model-estimated contribution from RO₂ to HO₂ during the measurement period ranged from 44 % to 69 % of ${\mathrm{HO}}_{\mathrm{2}}^{\ast }$. Calculations based on an observation-constrained chemical model revealed an overestimation of HO₂ and OH concentrations during warm periods of the field study. Sensitivity tests suggest that adding HO_x sinks or an HO₂ recycle process to the model could improve the model performance. Over-simulation of HO_x in the model resulted in overestimations of midday (10:00–15:00 UTC) production rates by more than 79 % for ozone and a factor of 1.88 for nitric acid. Our study highlights the need for further improving understanding of the sources and sinks of OH and HO₂ and representation of them in air quality models.