The invention discloses a navigation X-wave-band radar wave group detection method based on a wave theory. The navigation X-wave-band radar wave group detection method based on a wave theory includes the steps: performing empirical orthogonal function decomposition on a navigation X-wave-band radar image sequence, selecting a main modal to reconstruct a wave field, and obtaining the wave surface displacement of different positions in an observed sea area through scaling of the wave field; for the wave surface of one radial direction, utilizing change of the displacement gradient to detect the extreme value of the wave surface, and according to the difference between adjacent two maximum values and minimum values, obtaining the wave height at different positions; utilizing the sum of two sine functions to fit the wave surface between the adjacent minimum wave heights, and identifying the area as a wave group when the fitting parameter accords with the wave theory; and combining with observations at different times, obtaining the parameters of the wave group, such as amplitude, length and group speed. The navigation X-wave-band radar wave group detection method based on a wave theory utilizes the buoy to perform scaling on the main modal of the wave field so as to obtain the wave height information of a large area in the observed sea area, and then utilizes the two sine functions which are approximate in frequency based on the wave theory to determine the wave group without requirements for selecting a threshold according to the experience, and has the advantages of being simple and easy to do, and being wide in the application range.