Abstract: VOCs (volatile organic compounds), key precursors to the ozone pollutant, are indispensable parts of urban air quality modeling. Owing to their complex composition and the lack of monitoring data, understanding of their simulation accuracy is still poor. Here, simulations of VOCs in the Pearl River Delta region were performed using the nested grid air quality model prediction system (NAQPMS) from 21 September to 20 November 2017. First, monitoring of VOC concentrations from eight ground stations of the photochemical assessment monitoring stations was conducted to evaluate the accuracy of key VOC components. The results showed that the model has high simulation accuracy for toluene, ethylene, and xylene with concentration deviation ratios of 0.4%–26.6%, which can well reproduce the trend of daily average concentration and double-peak characteristics of diurnal variation. However, the model has a large simulation deviation for isoprene with strong chemical reaction activity and closed relation to plant emissions. The deviation ratio was nearly 100%, which cannot reproduce the diurnal variation characteristics of high concentration during the day and low concentration at night. The total amount of VOCs emitted by plants in the Pearl River Delta region was relatively high. Hence, ignoring the biological VOC emissions in the current simulation system can be the key reason for this simulation deviation. In addition, the results of simulation evaluation showed that the model still has great uncertainty in the VOC spatial distribution. With these, combining VOC experimental data with simulations to reveal and reduce the uncertainty of VOC simulations is necessary.