Abstract: Lagrangian-based methods are applied in this paper to get an insight into the transient sheet/cloud cavitating flows, including finite-time Lyapunov exponent (FTLE), Lagrangian coherent structures (LCS) and particle trajectory. Computational Fluid Dynamics (CFD) is used to obtain the cavitation flow structures. The turbulence model utilizes the Large Eddy Simulation (LES) approach and the interface mass transformation is modeled using Zwart cavitation model. Detailed analysis of cavitating structures with the LCS defined by the ridges of the FTLE show two main LCSs in sheet/cloud cavitation region,which are defined as leading edge (LE-LCS) and trailing edge LCSs (TE-LCS) respectively. Different interactions between the two LCSs indicate different flow structures in different cavitating developing stages.