The invention discloses a method and device for estimating the soil humidity of a vegetation coverage area, and belongs to the field of electronics, information and optical remote sensing. The methodcomprises the steps: firstly constructing a relation between an overall backward reflection coefficient and DDM reflection power through the data of a satellite-borne GNSS-R reflectometer; solving a vegetation reflection coefficient and an attenuation coefficient of the vegetation coverage area by utilizing the optical image data; fusing a relationship between a satellite-borne GNSS-R reflectometer data overall backward reflection coefficient and DDM reflection power and vegetation information in the optical data, and solving a relationship between a vegetation coverage area pure soil surfacereflection coefficient and the DDM reflection power; establishing a soil humidity and DDM reflection power regression model by utilizing the actually measured data of the soil humidity of the plurality of control points; and substituting GNSS-R data DDM reflection power of a certain point into the regression equation to invert the soil humidity. The implementation of the method is effective fusionof primary satellite-borne GNSS-R reflectometer data and multispectral remote sensing data images for jointly inverting the soil humidity of the vegetation coverage area.