Abstract: The changes and mechanism of internal dissipation of C/AL composite materials with different interfacial bonding strenglh after thermal cycling under external load are studied.It is fouad that the internal friction increases monotonically with the cycling numbers for C/L2 with relatively poor inierfzcial bornding,and this is mainly due to the local interfacial debonding.whereas,there is a peak at the curve of internal friction versus cycling numbers for C/LD2 wieh strong interfacial bonding,and this is mainly attributed to the break away of the dislocations.