Introduction: According to the metabolic characteristics of ultra-long-distance swimming and the characteristics of energy utilization and absorption during exercise, we have formulated a nutritional supplement plan for crossing to study the influence of swimming sports on blood sugar and give biochemical feedback indicators. Objective: To lay a foundation for studying the nutrition supplement rules during long-term exercise by taking the athletes’ blood after training to determine the changes in blood sugar, adjusting and determining the nutritional supplement plan during training. Methods: We monitor athletes’ physical function changes and biochemical indicators during training and study the changes of these biochemical indicators and athletes’ physical functions after long-term swimming exercises to scientifically arrange the exercise intensity and load during the training period. Results: The urine indexes after exercise did not change much, reflecting the exercise load's low intensity. The changes in blood lactic acid and blood urea indexes after exercise also confirmed this. During the training period, the athletes’ hemoglobin and red blood cell parameters are in the ideal range, indicating that the athlete's physical function is in good condition. During the training period, the training load intensity and load are reasonable according to ultra-long-distance swimming's energy supply characteristics. After training, the changes in blood glucose indicators reflect that the nutritional supplement program we formulated for athletes is reasonable and feasible. Conclusions: By monitoring the blood sugar and biochemical indicators of swimmers, it can help athletes to arrange exercise intensity scientifically and load during the training period, to better carry out open water competitions in China, and to arrange training and scientific nutrition during the training period scientifically. Lay the foundation for the establishment of nutrition supplement theory and training theory for super long-time sports. Level of evidence II; Therapeutic studies - investigation of treatment results.