Based on the data measured in 2009 in the DingXi, a typical semi-arid region in loess plateau, the temporal variation of condensed water and the influence factors are investigated. Meanwhile, the measurements of condensed water, made by weighing approach and eddy-correlation approach separately, are compared in this work. The results show that in the semi-arid regions in Loess Plateau, the daily maximum amount of condensation can reach 0.33 mm, the daily minimum recorded is 0.09 mm, and the average daily amount is 0.23mm. No obvious correlations is found between the amount of condensation and wind velocity, relative humidity, temperature, or land-air temperature difference. In the process of dew formation, the relative humidity which supplies the water vapor for condensing is an internal factor. The temperature which is motive power for condensing process is a key factor. The wind speed has an important effect and is an uncertain factor, which promotes but also can restrain the dew formation. It is also found that the following conditions favor the condensation process: wind speed of 0.5—2 m/s, relative humidity> 80% and land-air temperature difference <± 2℃.