The cold regions of western China are referred to as the “Asian Water Tower” and mainly include the Tibetan plateau and surrounding mountains. Its prominent hydrological feature is multiphase water transformation, which accelerates the water cycle and affects spatial and temporal patterns of water resources. Under the effect of lengthening ablation periods and increased annual precipitation, multiphase water transformation is accelerating. There are three main manifestations characterizing the transformation from solid to liquid water in the period since 1990: (i) the melting of glaciers has accelerated; (ii) the depth of permafrost active layers is increasing and their maximum freezing depth is decreasing; and (iii) a marked decrease in snowfall and increase in rainfall has been observed. The transformation from liquid to gaseous water was mainly concentrated on accelerating evapotranspiration. The transformation from gaseous to liquid water was observed as enhanced moisture recycling. The final hydrological effect of these transformations was observed in the change of the runoff components, increase in runoff, and lake expansion. A theory of multiphase water transformation is proposed, which is expected to contribute to the understanding of cold region hydrology in the future.