A defect in plate is imaged and located using modified RTM method with dispersive flexural wave, and the influences of the array parameters, such as the elements spacing and the array length or aperture, on defect imaging quality are investigated. The results show that the defect position acquired in simulation is consistent with its actual position, and the imaging quality is more sensitive to the receiving array parameters compared with the transmitting array parameters. In order to obtain a high quality image, the aperture of receiving array should be large enough, and the spacing of receiving array elements should be less than half-wavelength of flexural wave, namely, the spatial sampling theorem, which will provide guidance for the next experiments.