In the present work, the tip leakage vortex (TLV) in a mixed flow pump as turbine at pump mode is decomposed and reconstructed by Dynamic Mode Decomposition (DMD) for the first time. The flow field is solved by the k-omega SST turbulence model with validation of experimental data. The unstable primary tip leakage vortex (PTLV) can be mainly classified as two parts, oscillating PTLV-A and shedding PTLV-B. The evolution frequency of PTLV is 8.4f(i) (f(i) is the impeller rotating frequency). Results of DMD show that DMD can exactly decompose the dominant frequency of TLV evolution and its harmonic frequencies. The coherent structures captured by DMD mainly distribute near the trajectory of PTLV. Meanwhile, DMD can successfully reconstruct the flow field on basis of mean flow mode and the first mode. Proper Orthogonal Decomposition (POD) can also capture the main coherent structures of PTLV, due to the dominant frequencies of the most energetic modes contain the characteristic frequency of TLV. (C) 2020 Elsevier Ltd. All rights reserved.