Abstract: The Doppler pins system (Doppler pins system) array and high-speed photography are used to study the expansion and fracture behavior of single and double-layer metal cylindrical shells under detonation loading of hollow explosives(the total thickness of the two layers is equal to the thickness of the single layer). The velocity curves and high-speed photography images of the outer surface of the single and double-layer cylindrical shells are obtained. The results of velocity curves show that spallation occurs at about 2/5 of the outer surface of the single-layer cylindrical shell, and the remaining fragments of the single-layer cylindrical shell quickly catch up with the spallation cylindrical shell with incomplete separation after about 1.89μs and generate secondary impact loading. The inner and outer cylindrical shells of the double-layer cylindrical shell are separated rapidly because they cannot withstand the tensile stress. The outer cylindrical shell expands freely radially, and the inner cylindrical shell continues to catch up with the outer cylindrical shell after 26.13μs for a long time under detonation loading and undergoes secondary loading. The difference in secondary loading time is significant in the single-layer and double-layer expansion experiments. The premature separation of the double-layered cylindrical shell hinders the crack penetration from the inside to the outside, and delays the crack penetration until the complete fracture behavior of the whole cylindrical shell. Different from the traditional single-layer cylindrical shell fracture, the detonation product leakage time is late when the outer layer of the double-layer cylindrical shell expands, the fragment size of double-layer shell is obviously smaller than that of single-layer cylindrical shell, the overflowing detonation product distribution is relatively scattered and rare, and the overall crack of the outer cylindrical shell is clearly visible. The results of numerical simulation by SPH method show that the higher the spallation strength of single-layer cylindrical shells, the earlier the remaining fragments catch up with the spallation shell under secondary loading, and the more easily the penetrating fracture occurs. The gap blocking crack at the interface of double-layer cylindrical shells has a remarkable effect on the penetrating development of the cracks at the interface of double-layer cylindrical shells..