Disclosed is a first-order sea clutter detection method based on least squares approximation. The invention relates to a first-order sea clutter detection method, and aims to solve the problem that the found Bragg peak position is inaccurate and the false alarm rate is high in the prior art. The method comprises the following steps: calculating the theoretical Bragg frequency fB based on the working frequency f0 of radar, defining a noise zone on each sea element, and calculating the threshold of each sea element; detecting sea area sea state data according to the radar, determining the maximum radial velocity Vm of ocean current, and calculating the maximum Bragg frequency offset Delta fm; determining a search scope according to Delta fm and fB, determining a suspected point of the Bragg peak, confirming the threshold of the amplitude of the suspected point, and judging whether the current sea element is effective; for the effective sea elements, taking the neighboring points of an appropriate number of suspected points to form a point set, and acquiring the approximation function of the point set using a least squares approximation method; and finally, taking the peak point of the approximation function as a Bragg peak. The first-order sea clutter detection method is applied to the field of high-frequency ground wave radar detection.