The skin looseness of large-scale integral carbon/silicon carbide composite skeleton and skin structure in 165 dB thermal noise test was analyzed. The mechanism of skin looseness in noise and vibration environment was proposed， which was caused by the increase of breathing vibration amplitude of skin due to the large free hanging area of skin and skeleton assmbly.The simulation results show that the displacement response increase about 1.72 times with the increase of local free hanging area of the skin and skeleton under the same acceleration excitation. Three groups of flat plate test pieces with assembly clearance of 0.2， 0.6 and 1 mm are used to verify that the skin looseness problem is repeated. When the gap between the skin and the skeleton is large， the thickness of the adhesive layer is also larger. After several times of thermal loading， the adhesive performance of the adhesive layer decreases， and the air suspension phenomenon between the skin and the skeleton appears， which leads to the skin loosening under the vibration excitation. Finally， the improvement measures are put forward to ensure that the maximum gap between the large-scale skin and the skeleton is not more than 0.3 mm.