Abstract: This paper describes the work done on experimental measurements andmathematical modeling of solid particle concentration distribution in a three-phase gas-lift loop reactor. Air, water and sea sand were used as the experimental system. The distribution curves of solid particle concentration in the annular space and in the bubble layer above the top of the central tube were measured with a fibre optic sensor. A mathematical model for the axial distribution of solid particles in the annular space and an empirical model for solid particle concentration distribution in the central jetting zone of the bubble layer were derived respectively: The results calculated with these models were found to be in good agreement with the measured results.