This paper describes the numerical study on the cavitation problem of marine propellers by three-dimensional theory, based on the mathematical model of the trailing vortex geometry including the phenomena of the flow separation from the tips by using the vortex lattice method. The numerical procedure is developed to solve the partial-and super-cavitating propeller problem and to predict the cavity extent and the cavity thickness distribution. The results of the present numerical study are compared with the experimental results both in uniform and non-uniform flows. Although the comparison shows that the present method is advantageous to predict the cavity extent and the cavity thickness distribution, further problems still exist in the numerical studies to predict the propeller cavitation more accurately.