Abstract: From 1989 to 1992,quick weighing method,heat pulse technique,whole tree potometer were applied for many times together with steady state porometer to measure the transpiration of the poplar forests in Ningxia (Populus × xiaozhuanica cv. ‘Opera’) and in Shangdong (Populus deltoides cv.‘Lux’).The results showed that the values measured with steady state porometer were always higher than the actual values of transpiration while the values measured with the other three methods were believed to be close to the latter.The former were 1.3～3.2 (2.649 on average) times as high as the latter,varing with weather and plant conditions.So,the former values need to be adjusted with a coefficient.The correction coefficient would approximately be 0.3775 on an average,with 0.645 2 in arid area and 0.340 7 in more humid area.