Air pollution, particularly PM_2.5, is a significant public health concern in China and worldwide. The diurnal fluctuation feature of PM_2.5 is a crucial factor influencing human exposure, but research on its spatiotemporal characteristics across China is limited. This study aims to explore the spatial patterns of diurnal variations in PM_2.5 concentrations across China and identify the factors that influence them. We conducted a comprehensive study to investigate the diurnal range of PM_2.5 concentration and meteorological factors from 1636 fixed monitoring sites in China from January 2015 to December 2021. We calculated the average diurnal variation of PM_2.5 during different seasons at each site and explored the correlation between the diurnal variation of PM_2.5 and various types of factors. The main influencing factors was identified by employing eXtreme Gradient Boosting (XGBoost) and SHapley Additive exPlanations (SHAP). Our spatial analysis revealed significant variations in both the mean concentration and diurnal range of PM_2.5 across different regions in China. The main factors affecting the diurnal variation of PM_2.5 include topographic factors such as elevation, meteorological factors such as temperature, air pressure, and dew point temperature, and socioeconomic factors such as industry and transportation. This study is beneficial for evidence-based policy decisions aimed at reducing air pollution and protecting public health.