There remains uncertainty on effects of climatic warming on crop phenology and biomass on the Tibetan Plateau. A field warming experiment was conducted in a maize system located at the Dazi county of the Tibet since late April, 2015. This study examined the effect of warming on maize phenology (i.e. sowing time, seeding stage, trefoil stage, five-leaf stage, jointing stage, pustulation period, milk-ripe stage, mature period), aboveground biomass and plant height. The trefoil stage and five-leaf stage completed 2 days earlier; the jointing stage completed 1.3 days earlier (t=2.00, P=0.184), the pustulation period completed 3.3 days earlier (t=2.00, P=0.184), the milk-ripe stage completed 4.7 days earlier (t=2.80, P=0.119), and the mature period completed 6.7 days earlier (t=3.78, P=0.050 2) under experimental warming conditions. Experimetal warming shorten 6.7 days of the interval between seeding stage and mature period (t=2.77, P=0.050 2), and 3.3 days of the interval between pustulation period and mature period(t=2.43, P=0.122). Experimental warming increased cumulative temperature by 11.89 ℃ during the period from sowing time to seeding stage (t=11.21, P=0.000), decreased cumulative temperature by 7.58 ℃ during the period from seeding stage to trefoil stage(t=77.55, P=0.000). However, experimental warming had no obvious effects on cumulative temperature during the period from trefoil stage to five-leaf stage, from five-leaf stage to jointing stage, from jointing stage to pustulation period, from pustulation period to milk-ripe stage, from milk-ripe stage to mature stage, and from sowing stage to mature stage. Experimental warming had no significant effects on aboveground plant biomass and plant height. Therefore, warming may alter maize phenology but did not significantly affect aboveground plant biomass.