A fast method to measure the primary surface dynamic deformation of a radio telescope for improving high-frequency observation efficiency is proposed based on the similarity and overlap of the multibeam patterns, and the phase retrieval method. Firstly, the pointing offsets relative to the center are subtracted from a part of in-focus and defocus patterns of each beam, and these patterns are spliced to construct a group of complete in-focus and defocus patterns of the center beam. Secondly, the sum of squared residuals by which the splicing patterns differ from the theoretical ones is minimized based on Levenberg-Marquardt algorithm, to calculate the coefficients of Zernike polynomials, and the primary reflector dynamic deformation is retrieved. The numerical simulation experiment based on the 7-beam Q-band shows that the proposed method can retrieve the primary reflector dynamic deformation of the radio telescope in 5 min with the measurement accuracy of 55 μm, with the advantages of anti-noise and anti-fluctuation, and can be applied for the astronomical observations below 90 GHz.