The invention discloses a 300m-grade high rock-fill dam material parameter inversion method based on GBSAR appearance monitoring. The method comprises the following steps: 1, respectively erecting four portable foundation radar interferometers at the left banks and the right banks of the upstream side and the downstream side of a 300m-grade high rock-fill dam, and respectively obtaining SAR images of the surface of a dam body from four orientations; 2, performing image processing on the SAR images so as to obtain surface deformations of the dam body from the four orientations, and performing three-dimensional parsing on the surface deformations of the dam body to obtain deformation values of the surface of the dam body in a rive direction, a horizontal direction and a vertical direction; and 3, by use of actually measured appearance deformations in three directions, establishing an object function by use of different weights, and performing inversion analyzing on rockfill body intensity deformation parameters of the 300m-grade high rock-fill dam. According to the invention, dam body surface deformation data with submillimeter-grade precision is obtained by use of GBSAR; and rockfill body partitioning and the evolution process of the parameters along with time are taken into consideration in parameter inversion, the inversion object function is established, and the accuracy of the parameter inversion of the rockfill body of the 300m-grade high rock-fill dam is guaranteed.