The dynamic analysis of the 750Kw wind turbine blade was presented based on Reverse Engineering. Because of complex shape, the model of wind turbine blade is a bottleneck of restriction development on the dynamic characteristic research of blade. The work attempted a new way to build the blade 3D model and completed the dynamic analysis. At first, the point cloud data of blade were gained using ATOS optical scanner. Secondly simplified, smoothed and partitioned in Imageware, point cloudy data were created into curves. Then the curves were imported into UG, the 3D model of blade was attained through curve fitting. At last the dynamic analysis of the blade was completed in ANSYS Workbench. The analysis adopted BlockLanczos method to extract the mode and get the natural frequency and eigenmode from the first to sixth modes. The paper ascertained the first and second wave eigenmodes, the first swing and the first torsion eigenmode. Calculations showed that eigenvalue of wave vibration and swing vibration were lower, torsion vibration eigenvalue was higher. In the vibration of the blade, the couple vibration of wave and swing taked major role, and the influences of torsional vibration were not great. The results showed the wave and swing vibration were predominated, the torsional vibration can be neglectful. The paper developed some new methods, established foundations for the further research of large wind turbine blade in the future.