Plant transpiration is an important part of water cycle in ecosystem, that is, the process of water transfer from soil to atmosphere through plants. It is driven by solar radiation, air temperature, air humidity and wind speed, and also affected by soil water storage capacity. Understanding and quantifying the influence mechanism of transpiration is an important basis to explore the water consumption of vegetation and the water balance of ecosystem. However, although the climate conditions in the subtropical karst area are good, there is a drought period of 4-5 months. At the same time, plants are often affected by water stress because of the thin soil layer and low water holding capacity of soil in karst area. The study of plant transpiration characteristics helps us understand the water consumption of trees in subtropical karst areas, and is also of great significance for exploring the impact of climate and hydro-geological conditions on plant transpiration. Granier's thermal dissipation probe method was used to continuously monitor the trunk sap flow of the evergreen tree species (L.lucidum) and the deciduous tree species (R.pseudoacacia) in the secondary forest in the subtropical karst area. The meteorological factors and soil moisture content (SMC) are also monitored simultaneously. Our purpose is to analyze the transpiration characteristics of two life-form tree species and their responses to environmental factors on different time scales. The results show that:(1) at the seasonal scale, the main factors affecting the whole-tree transpiration (ET) are solar radiation intensity (Rs), air temperature (T) and vapor pressure deficiency (VPD). The transpiration of L.lucidum (ET_L) is shown as summer (1.29 kg/h) > spring (0.57 kg/h) > winter (0.15 kg/h) > autumn (0.13 kg/h), transpiration of R.pseudoacacia (ET_R) is shown as summer (0.90 kg/h) > spring (0.31 kg/h) > autumn (0.16 kg/h) > winter (0.04 kg/h). (2) On the daily scale, the ET of the two tree species shown obvious single peak curve on sunny day, and the main factors affecting transpiration are T, VPD and Rs. However, due to the differences in the physiological characteristics of evergreen and deciduous tree species, ET_L is weakened during rainfall, while ET_R is significantly increased. (3) in terms of day and night, the nocturnal transpiration of the two tree species accounts for less than 35% of the total daily transpiration on average. Affected by the phenomenon of night precipitation and the physiological characteristics of trees, the proportion of nocturnal transpiration in the autumn and winter is significantly higher than that in the spring and summer. At the same time, the average daily nocturnal transpiration and its proportion of R.pseudoacacia (1.56 kg, 24.1%) is higher than that of L.lucidum (1.08 kg, 13.9%).