This paper extends the double linearization theory to three-dimensional supersonic cascades to study the spa wisely nonuniform mean loading effects upon unsteady aerodynamic forces of vibrating blades. The theory takes account of the unsteady shock displacement effect and the two kinds of unsteady spanwise aerodynamic forces due to nonuniform mean loadings and nonuniform vibration amplitudes in the three-dimensional flow field. Numerical examples show several features of unsteady aerodynamic responses which are ascribable to the effects of the spanwise nonuniform angle of attack, camber and thickness. The nonuniform effects of the camber and thickness are greater than those of the angle of attack. In order to obtain a large total steady lift coefficient on a stability boundary for the first bending mode, the cascade configuration with the angle of attack decreasing and the camber and thickness increasing from hub to tip is advantageous.