Nutrient availability plays vital roles in phytoplankton growth and might, to a large extent, affect their thermal response, thus tremendously influencing marine primary production and biogeochemical cycles in the projected global warming. As one of the dominant phytoplankton, diatoms contribute around 20% of global primary production and generate a large amount of organic carbon and oxygen that serve as food and essentials for life on the earth. To determine whether the ambient nutrient concentration affects the thermal responses of diatoms, we conducted a series of short-term thermal and nutrient manipulation experiments on two dominant diatoms, Pseudo-nitzschia sp. and Leptocylindrus sp., in the subtropical coastal regions. We then verified the results with 17-year long-term monitoring data. Our result indicates that nutrient-enriched ambient environments benefit diatom to adapt to ocean warming, as evidenced by their increasing optimal growth temperature and population maximum growth rate. These add to our knowledge of global and regional-scale diatom thermal response in the future ocean, such as intensifying the nutrient-impoverishment in oligotrophic oceans and nutrient-enrichment in coastal areas.