According to the spatial features of environmental actions, on the basis of the spatial multi-scale model framework (including the global environment, regional environment, engineering environment, surface environment and internal environment of concrete) and the mathematic model for environmental actions, the spatial multi-scale relative humidity values for concrete structures were studied. That is, based on the influential factors of relative humidity on the different spatial scales, the relative humidity values in concrete were deduced by adjustment step by step from the values on the global environment to the regional environment, the engineering environment and the surface environment of concrete. It was found that using the superposition method of conventional statistic model and spatial residual error, the quantitive relationship of relative humidity values in the regional environmental scale and the engineering environmental scale can be established effectively. Moreover, the relative humidity values on the surface of concrete structural elements are related with the temperature values on the surface of concrete structural elements, and the difference of relative humidity values between the surface and the inner part of concrete should be considered in the durability assessment of concrete structures.