Abstract: Bubble sizes and gas hold-up are important parameters of flotation column.bubble sizes and local gas hold-up in downflow pipe of LHJ column were determined with electro-optical probe method in this paper.the affection of bubble sizes and local gas hold-up of LHJ column by column structure parameters and fluid physic-chemical parameters was investigated. The results showed that fluid pressure,radial and axial position of downflow pipe, pH and dosage of frother all have effection on the bubble sizes and local gas hold-up, and that addition of frother can obviously decrease the mean bubble size and mean while increase the gas hold-up.