Sea cucumber is a traditional nutritious marine food and an important economic aquatic product in China. Sea cucumbers are vulnerable to autolysis, and most sea cucumbers require processing before distribution and consumption. Therefore, processing is a critical sector in the industry chain of sea cucumber. Clarifying the change in the composition and food structure of sea cucumber during processing is the key point for understanding the mechanism of sea cucumber product quality, and would direct the rational development of novel technology for the high-quality processing of sea cucumber. It is thus considered as a key scientific issue related to the development of the sea cucumber industry. In this review, the composition and food structure features of sea cucumbers were overviewed, and the major processing procedures of sea cucumbers were summarized. Based on this background, the changes in composition and food structure of sea cucumber during the processing, including boiling, drying, rehydration, enzymatic hydrolysis, and ready-to-eat sea cucumber processing were introduced, and the recommendations for further research were provided. It would be beneficial for accelerating the solution of the above scientific issue, and contribute to the high-quality development of the sea cucumber industry.