The sea-sky line is an important feature of sea and air background images, and its detection plays an important role in the division of sky and sea areas and target detection. However, sea clutter, clouds, strong reflection, and dynamic weather conditions in the complex sea and air background environment make it difficult to detect the sea-sky line. This paper aims to address the environmental adaptability problem of sea-sky line detection in a complex background. Three aspects were analyzed in detail: the characteristics of the original image obtained by the visual sensor and those of the sea-sky line in the image; interference factors and their suppression methods; existing methods of generating the sea-sky line. Furthermore, their advantages, disadvantages, and applicable scenarios were elaborated through comparative experiments, and the proposed morphological methods were experimentally compared. Finally, the future challenges and research directions of sea-sky line detection were discussed.