Whitefly (Homoptera: Aleyrodidae) is among the most important crop pests around the world. Recent work has focused on obtaining basic ecological information about whiteflies for the development of non-chemical techniques to control these insect pests. In this research, a series of experiments were designed to clarify the ecological characteristics of whiteflies in Hebei Province in northern China in 2012. Two whitefly species, Trialeurodes vaporariorum (Westwood) and Bemisia tabaci (Gennadius) biotype Q, were investigated in the experimental greenhouses. The adults of these mixed whitefly populations displayed two activity peaks: one in the morning (09:00–11:00) and the other in the afternoon (15:00–16:00), with a tranquil period at night. The proportions of the two whiteflies at different leaf positions changed dramatically between the spring and autumn. The proportion of adults in the middle leaf position increased for both species in autumn compared to spring. The majority of T. vaporariorum moved downwards, whereas the B. tabaci moved upwards in autumn compared to their distributions in spring. The within-plant distribution of B. tabaci was more closely related to the leaf positions than leaf ages. In contrast, T. vaporariorum was more associated to leaf ages than leaf positions.