Spout diameter is considered an important parameter in gas-solid spouted bed which needs to be identified. Many operating variables can be effected the determination of the spout diameter in gas-solid spouted beds. Five operating variables have been chosen to study the effect of them on the spout diameter (solid density, static bed height, particle diameter, superficial gas velocity and inlet diameter). These were chosen based on the appearing in correlations found in the literature to calculate the spout diameter of conventional spouted beds. In this study, the effect of operating variables on the spout diameter have been performed experimentally using a new advanced gas-solid optical fiber probe technique that has been developed in collaboration with the Chinese Academy of Sciences. As well, a statistical analysis of the experimental data has been used to validate the factorial analysis of experiments using MINITAB17 statistical software program. It was found that all five operating variables together with the interaction between particles size and inlet diameter, and gas velocity and inlet diameter, have a significant effect on the determination of spout diameter. Regression analysis was performed to obtain a correlation which could identify the average spout diameter in the gas-solid spouted beds. The obtained regression correlation was able to predict closely the average spout diameter when compared with the experimental results.