The separation process of leading edge vortices (LEV) from an unsteady pitching plate is studied. The analysis processes a large amount of data from the two dimensional (2D) simulation of a at plate undergoing a 45° pitch-up maneuver. Large scale lift loss on the plate is shown to correlate with the vortex shedding. A Lagrangian coherent structures (LCS) analysis, including hyperbolic LCSs, Lagrangian-Averaged Vorticity Deviation (LAVD), and both FTLE saddle and λ-saddle are all applied around the LEV to identify the vortex dynamics. This is compared with a calculation of the circulation and the vortex shedding mechanism (VSM). The identified LEV dynamics revealed by multiple vortex criteria match with the circulation development and lift history in time, suggesting that LEV separation is a good model for various vortex shedding mechanisms.