Abstract: With some silk threads being planted on the shoulder of the inlet and the silk-thread flow visualization method being used, the starting characteristics of an inward-turning inlet were researched in hypersonic cold-flow blow-down wind tunnel experiments. The experiments were carried out in a Φ0.5 m hypersonic wind tunnel of China Aerodynamics Research and Development Center (CARDC). The Mach number of the experiments was 5. The inlet was an elliptical-to-circle cross-section transition inlet with a total contraction ratio of 5.8, an internal contraction ratio of 1.7 and a diameter of 50 mm at the throat round-section. The recommended length of the silk-thread and the recommended interval of the adjacent silk-thread, both of which influence the visualization effect of the silk-thread flow, were obtained through the experiments. The results show that the visualization method can quickly, accurately, intuitively, and convenintly judge the real-time starting state of the inward-turning inlet in the experiments, and can obtain the initial position of the separation and the flow structure of the separation zone when the inlet does not start. The results also show that the current inward-turning inlet has double states at Ma=5. A feasible way for the inlet to restart or quit unstarting was given. At the same time, the research shows that the current silk-thread visualization method enriches the flow visualization method library, especially for the starting characteristics research of the inward-turning inlet in wind tunnel experiments.