A simulation method by air and space integrated fusion based on hyper-/multispectral imagery is proposed. The transformations of spectra, scale-space, radiative intensity, mixed pixel, noise are adopted in the simulation method on the basis of aviatic multispectral imagery according to parameters of space multispectral imagery, and certain ground objects in the aviatic hyperspectral imagery are mapped into the space multispectral imagery to obtain simulative space multispectral imagery for these ground objects through the simulation method. Experimental results demonstrate that the simulation method is effective and easy to implement; the heavy workload on model establishment of three-dimensional scene and sensor response is reduced in this simulation method; it is successful for the method to simulate space multispectral imagery of certain ground objects. A new domain on simulation method of remote sensing imagery is developed. This simulation method is valuable in research and application.