The invention relates to a novel flotation column serial connection test system for improving the flotation granularity upper limit. The equipment of the system comprises a fed material stirring barrel, a feeding pump, a feeding pressure meter, a froth generator, a primary-section foam enriching chamber, a lower catheter, a spray type flotation column chamber, a primary-section tailing box, a secondary-section foam enriching chamber, a column flotation chamber, a rotary flow sorting chamber, a circulation ore pulp pump, a circulation pressure meter, a froth generator, a secondary-section tailing box and an FCMC cyclo-microfroth flotation column, wherein a spray type flotation column and the FCMC cyclo-microfroth flotation column are connected in series by the system, and the primary-section tailing is used as secondary-section fed materials. The system is favorable for the static fast flotation of preference flotation of coal with good flotation performance and the strong power efficient recovery of difficult-to-sort coal, in addition, the problem of high-concentration coal slime flotation can be perfectly solved, the recovery rate of coarse particle coal slime can be improved, and the problem of coarse particle running of coarse particle flotation can be solved.