A medical scanning system and method for determining scanning parameters based on a scout image, the system includes: a scanned object description module for describing the shape of a scanned object on an initial image; an adjustment module for aligning the shape of the scanned object with the pre-stored average shape; a principal component analysis module for extracting the principal component for the aligned shape of the scanned object; a desired shape acquisition module for imparting weight parameters to said principal component, acquiring a plurality of new shapes, and from said plurality of new shapes, determining the new shape with the maximum cost function value as the desired shape and a scanning parameter setting module for setting scanning parameters based on the desired shape.