Alpine timberline,as the most foundational ecological boundary for tree species growth under extremely environmental conditions,has received increasing attention in global change research given its potential sensitivity to climate change. An increased understanding on formation mechanism of timberline and associated physio-ecological characteristics of plants is of great importance in forecasting vegetation dynamics under future climate change. Two scientific questions concerned in timberline formation research are: （1) how environmental conditions do affect the growth and distribution of tree species at the timberline,and what is its intrinsic mechanism？（2）what is the advantage of shrubs and grasses compared with trees at the timberline,and what is the ecological function and significance of the variation of life form from trees to shrubs and grasses? This paper reviewed the latest progress on formation mechanism of timberline and related physio-ecological characteristics of plants. A line of literatures have confirmed that temperature,especially low temperature during the growing season,can be used to explain the position of high altitude timberline at a global scale,however,the mechanisms controlling growth and survival of tree species are not properly understood. There are mainly two contradictory views,i.e. carbon limitation and growth limitation hypotheses. The observed responses of timberline to climate change,especially global warming,are also not consistent at the global scale,suggesting that the effect of global change on distribution of timberline and plant growth is rather complicated and uncertain. Therefore,future research should pay more attention to physio-ecological processes related to plant growth at timberline,such as water or nutrient use processes. In order to have a much better understanding on timberline formation and its response to future climatic change,the ecological function and significance of life-form transitions should receive particular attention.