Aiming at the problem of low clarity of images obtained by the coastal sea area monitoring system under dense fog conditions, a sea area image defogging algorithm based on improved bright channel and guided filtering is proposed. First, the L channel of the Lab color space is used as a guide map to estimate the atmospheric light value through fast guided filtering of the original image. Then, the bright channel transmittance function can be obtained by using the bright channel prior theory based on the atmospheric light. Finally, an improved weighted guided filter is introduced to optimize the transmittance function of the bright channel，thus obtaining the final transmittance function, which is brought into the atmospheric scattering model to achieve image defogging，and gamma correction was performed on the results of defogging. The experimental results show that the visual effect of image defogging results are obvious, which can effectively reduce the loss of detail information and improve the clarity of the image. Compared with the optimal results of the classical algorithm, NIQE, contrast and information entropy are increased to 10.92 %, 4.12 % and 4.37 %. It has certain theoretical value and practical significance for perfecting the coastal waters monitoring system.