Water-retaining pavements are optional and effective to mitigate urban heat island as they stay cool by holding rainwater at the surface layer for evaporation cooling. However, excessive rainfall falling on such pavements will overflow and thus contribute to flooding. Here, we report a novel drainable water-retaining paver block for mitigating urban heat island and simultaneously reducing runoff. The albedo, temperature, water-retaining capacity, and outflow sensible heat of this novel paver block were measured and compared with those of a dense block and a pervious block. The permeability of the water-retaining block was also measured to examine whether this paver block can avoid overflow during heavy rain. Our results showed that the temperature of the water-retaining block in the wet condition can be reduced by 13 °C in the daytime and 3 °C at night, which indicates its good performance of cooling the local air temperature. Our results also indicated that the permeability of the water-retaining block is two orders higher than the precipitation rate of heavy rain, which reveals the excellent performance of quickly draining the excessive water in case of heavy rain.