1. A method for correcting a shimming device, the method comprising: acquiring a phase image in a coronal plane direction of a phantom for each test position of the shimming device; extracting an internal contour line in the phase image; mapping the internal contour line onto a rectangular coordinate system or a polar coordinate system to obtain a corresponding characteristic curve; estimating a degree of symmetry of the characteristic curve, such that an image symmetry estimation for the test position is obtained; and selecting the test position with an optimized image symmetry estimation as an optimum deployment point of the shimming device.