The induction time or sliding time can be used to characterize the hydrophobicity of mineral particles. In order to investigate the relationship between sliding process and induction time, the Induction Timer and high-speed camera technology were adopted in this study. It was found that the flotation recoveries of low rank coal particles increased with the surfactant concentration increase. Howerer, the analysis results of induction time and slip angle velocity indicated that the flotation performances of low rank coal were depressed by anion SDS surfactant. Therefore, the slip angle velocity results can be adopted to support the induction time measurements.