This paper examines the natural frequencies and modes of cracked Mindlin plate using the Ritz method based on the Mindlin plate theory. The vibration characteristics of cantilever Mindlin plate with a side crack are presented, and the effect of the side crack on the natural frequencies and modal function of Mindlin plate is also investigated. In this analysis, a special mode shape function composed of two parts is employed, where one part is the ideal mode shape of intact Mindlin plate obtained by the beam function combination, and the other part is the corner function which uses the vertex singularity theory to construct the expression of deflection and rotation discontinuity along the crack. The results of the Mindlin theory obtained by a high-precision numerical software of Maple is then compared and verified against the data from finite element simulation by ANSYS.