A new model is presented to elucidate the optical-ultraviolet ''flickering'' variability in cataclysmic variables. In this model, light fluctuations are produced by occasional flarelike events and subsequent avalanche Bow in the accretion disk atmospheres. Flares are assumed to be ignited when the mass density exceeds a critical density. The disk then evolves to and stays at a self-organized critical state, in which seemingly chaotic fluctuations can be produced. We calculated fluctuating light curves by cellular-automaton simulations. The resultant power spectral density (PSD) consists of a flat part [S(f) proportional to f(0), where f is frequency] at lower frequencies and a steep-decline part [S(f) proportional to f(-beta), with beta similar or equal to 1-2] at higher frequencies. It is important that the PSD is rather insensitive to wavelength.