Past studies have demonstrated the remarkable energy-saving effect of vertical greenery systems. The vast majority of these works focus on opaque building walls. While external shadings on windows are more effective than these on walls. Inspired by the climbing plants (vines) raised outside windows by residents, the present study proposed the design of movable green window shading systems (MGWSS) that can shade beam solar radiation but allows soft daylighting. On the basis of simplified MGWSS models, experiments were conducted in summer to evaluate the shading performance with three plant species. First, the energy-saving effect and climatic data were measured for test rooms with west-facing windows. The results indicated that the presence of green shading reduced the impact of solar radiation on the cooling energy consumption with the correlation coefficients from 0.94 to 0.61. Then, the shading coefficient, which is a key parameter for energy saving, was measured by a new technique using photovoltaic panels. The correlation between the coverage rate and the surface-averaged shading coefficient was established. The results showed that when the coverage rate of the MGWSS with Dishcloth gourd was 80%, the shading coefficient was 0.28, and the cooling energy consumption and heat flux transferred through the window glass were reduced by 11.5% and 64.8%, respectively. The shading characteristic was investigated using the instantaneous data. It found that stronger ambient solar radiation resulted in better shading performance (lower shading coefficient). For a west-facing window, the best shading performance was found at oblique solar incidence angles.