Nowadays electric power quality problems such as flicker (voltage fluctuation) are major concerns of electric companies and industrial consumers. Identification of flicker sources is an important stage in the flicker reduction process. Flicker source can be modeled as a nonlinear load whose admittance is intermittent and time-variant. In the steady state, fluctuation of voltage amplitude is a function of the impedance of flicker sources. In this paper, after calculating the gradient of voltage amplitudes and constructing a Jacobian matrix, criteria for flicker source detection are proposed. Therefore, by measuring voltage and current of each load in the power system, the contaminative loads are identified. In the next step, flicker propagation throughout the power system is investigated. For identifying the dominant flicker source, an algorithm based on a directed graph method is proposed. For different operation modes of flicker sources, the effects of their locations on dominating are analytically interpreted. The proposed methods are tested in a typical nonradial power system in which several flicker sources have been operated. The flicker sources are operated with equal fluctuation frequency and different operation modes. Simulation results show a good performance for the single point proposed method in flicker source detection. These results confirm that the proposed algorithm can identify dominant flicker source as expected for our theory.