Urbanization and climate change are significantly increasing urban flood frequency and severity, threatening socioeconomic stability and human safety. This study analyzes flood flow trends in major Chinese provinces using high-resolution data. It identifies climate change and urbanization contributions to flood risk via panel regression and assesses the spatiotemporal coupling of flood risk and population exposure. Results show regional differences in flood flow trends, with increases in the southeast coastal and South China regions and decreases in the northwest and North China regions. Extreme rainfall events are the main factor exacerbating urban flood threats. The coupling between flood risk and population exposure has intensified, especially in the Yangtze River Delta and Pearl River Delta regions. This study highlights the need to incorporate flood risk into urban planning and climate change adaptation strategies.