Based on experiments with single air bubbles rising in stagnant non-Newtonian fluids, an innovative model containing the aspect ratio (E) and two parameters (alpha, beta) was proposed and proved to be capable of characterizing the bubble shape from spherical/ellipsoidal to prolate/oblate-tear with good accuracy. Several impacts on bubble deformation were investigated, involving the rheological properties of the fluids and different forces exerted on the bubble, which were quantified by multiple dimensionless numbers (e.g., Reynolds, Eotvos, and Deborah number). Within a wide range, the empirical correlations were obtained for parameter beta, and between alpha and beta. Together with the shape model, a complete system was set up for bubble shape characterization and prediction that will provide new ideas for future studies on bubble hydrodynamics.