An embodiment of the invention provides a land surface emissivity calculating method and device. The method comprises the following steps: a land surface emissivity calculation result of an object land surface is obtained via a land surface emissivity model, the calculation result is compared with a microwave land surface radiant ratio of the object land surface, land surface parameters and/or parameters of the land surface emissivity model of the object land surface are adjusted according to a comparison result, and land surface emissivity of the object land surface is determined according to adjusted land surface parameters of the object land surface. Via comparison and optimization, the land surface parameters and model parameters of the object land surface are adjusted, accuracy of the emissivity of the object land surface is improved, and accuracy of numerical weather prediction is correspondingly improved.