There is provided a surface microstructure measurement method, a surface microstructure measurement data analysis method, and an X-ray scattering measurement device which can accurately measure a microstructure on a surface and which can evaluate a three-dimensional structural feature. In the surface microstructure measurement method, the specimen surface is irradiated with X-ray at a grazing incident angle and a scattering intensity is measured; a specimen model with a microstructure on a surface in which one or more layers is formed in a direction perpendicular to the surface and unit structures are periodically arranged in a direction parallel to the surface within the layers is assumed; a scattering intensity of X-ray scattered by the microstructure is calculated in consideration of effects of refraction and reflection caused by the layer; and the scattering intensity of X-ray calculated by the specimen model is fitted to the measured scattering intensity. Then, as a result of the fitting, an optimum value of a parameter for specifying the shape of the unit structures is determined. Therefore, it is possible to accurately measure a microstructure.