With the development of offshore oil and gas resources, hydrates pose a significant challenge to flow assurance. Hydrates can form, accumulate, and settle in pipelines, causing blockages, reducing transport capacity, and leading to significant economic losses and fatalities. As oil and gas exploration moves deeper into the ocean, the issue of hydrate blockages has become more severe. It is essential to take adequate measures promptly to mitigate the hazards of hydrate blockages after they form. However, a prerequisite for effective mitigation is accurately detecting the location and amount of hydrate formation. This article summarizes the temperature–pressure, acoustic, electrical, instrumental–response, and flow characteristics of hydrate formation and blocking under various conditions. It also analyzes the principles, limitations, and applicability of various blockage detection methods, including acoustic, transient, and fiber-optic-based methods. Finally, it lists the results of field experiments and commercially used products. Given their advantages of accuracy and a wide detection range, acoustic pulse reflectometry and transient-based methods are considered effective for detecting hydrate blockages in future underwater pipelines. Using strict backpressure warnings combined with accurate detection via acoustic pulse reflectometry or transient-based methods, efficient and timely diagnosis of hydrate blockages can be achieved. The use of a hydrate model combined with fiber optics could prove to be an effective method for detecting blockages in newly laid pipelines in the future.