The retraction of the edge of an initially discotic liquid sheet and the formation of a rim at the edge, the process, which is a precursor of atomisation of liquid, is simulated by a Front-Tracking/Finite Difference method. The shape of the rim depends on the Ohnesorge number, which represents the viscosity of the sheet. The edge retraction speed approaches asymptotically the viscous velocity scale as the Ohnesorge number increases. As the Ohnesorge number decreases, on the other hand, the retraction speed approaches asymptotically the inertial velocity scale, which is known as Taylor-Culick velocity. This asymptotic behaviour is identical with the case of a two-dimensional planer liquid sheet.