Dew plays a crucial role in ecosystem processes in arid and semiarid regions, and is expected to be affected by climate warming. However, how warming simulation affects dew formation has been long ignored and rarely addressed. We measured dew amount and duration and plant traits related to dew condensation from 2012 to 2017 in a long-term infrared warming experiment in an alpine grassland of Tibetan Plateau. The results showed that (1) warming reduced the dew amount by 42%-91% and reduced dew duration by 32 days compared to the ambient condition. (2) Plant functional groups differed in dew formation. (3) Under the warming treatment, the dew amount decreased with plant height; while under the ambient conditions, the dew amount showed the opposite trend. Warming using an infrared heater system greatly reduces dew formation, which if overlooked, could lead to overestimation of climate warming impacts on ecosystem processes.