Particle concentration is an important parameter describing the flow state of gas-solid two-phase flow. In this paper, the relationship between the particle concentration and the output capacitance signals of the ECT sensor is derived, and the on-line nondestructive particle concentration measurement approach is studied to detect the two-phase flow. The simulation experiment of particle concentration measurement is performed using COMSOL and MATLAB, by which the accuracies of the image-based and capacitancebased particle concentration measurement approaches are quantitatively evaluated. A preliminary experimental study on particle concentration measurement of gas-solid two-phase flow is carried out in a circulating turbulent fluidized bed, and the experimental results show that the image-based particle volume concentration measured at the bed height of 200, 300 and 400 mm fluctuates in the range of 0. 26~ 0. 75, 0. 09~ 0. 33, 0. 04~ 0. 31, respectively, while the particle volume concentration measured by capacitance-based method is in the range of 0. 27~ 0. 68, 0. 09~ 0. 47, 0. 04~ 0. 26, respectively.