Hong Kong, as one of the densely populated metropolises in East Asia, has been suffering from severe photochemical smog in the past decades, though the observed nitrogen oxides (NO<sub>x</sub>) and total volatile organic compounds (TVOCs) were significantly reduced. This study, based on the observation data in the autumns of 2007, 2013 and 2016, investigated the photochemical ozone (O<sub>3</sub>) formation and radical chemistry during the three sampling periods in Hong Kong with the aid of a Photochemical Box Model incorporating the Master Chemical Mechanism (PBM-MCM). Neither the observed O<sub>3</sub> nor the simulated locally produced O<sub>3</sub> changed significantly (<i>p</i>=0.11 and 0.99, respectively) from 2007 to 2013; however, both of which decreased (<i>p</i><0.05) from the VOC sampling days in 2013 to those in 2016 at a rate of −5.04±0.05 and −4.35±0.10 ppbv yr<sup>−1</sup>, respectively. The regionally transported O<sub>3</sub> showed an increase (rate=1.62±0.39 ppbv yr<sup>−1</sup>, <i>p</i><0.05) during 2007–2013, but slight decrease (<i>p</i>=0.09) from 2013 to 2016. The mitigation of autumn O<sub>3</sub> pollution in this region was further confirmed by the continuous monitoring data, which has never been reported in previous studies. Benefited from the air pollution control measures taken in Hong Kong, the local O<sub>3</sub> production rate decreased remarkably (<i>p</i><0.05) from 2007 to 2016, along with the lowering of recycling rate of hydroxyl radical (OH). Specifically, VOCs emitted from the source of liquefied petroleum gas (LPG) usage and gasoline evaporation decreased in this decade at a rate of −2.61±0.03 ppbv yr<sup>−1</sup>, leading to a reduction of the O<sub>3</sub> production rate from 0.51±0.11 ppbv h<sup>−1</sup> in 2007 to 0.10±0.02 ppbv h<sup>−1</sup> in 2016. In addition, solvent usage made decreasing contributions to both VOCs (rate=−2.29±0.03 ppbv yr<sup>−1</sup>) and local O<sub>3</sub> production rate (1.22±0.17 and 0.14±0.05 ppbv h<sup>−1</sup> in 2007 and 2016, respectively) in the same period. All the rates reported here were for the VOC sampling days in the three sampling campaigns. It is noteworthy that meteorological changes also play important roles in the inter-annual variations of the observed O<sub>3</sub> and the simulated O<sub>3</sub> production rates. Evaluations with more data in longer periods are therefore recommended. The analyses on the decadal changes of the local and regional photochemistry in Hong Kong in this study may be a reference for combating China’s national-wide O<sub>3</sub> pollution in near future.