The recovery rate of micro-fine cassiterite in a complex polymetallic tin ore in Yunnan has long been low, seriously restricting the improvement of comprehensive beneficiation indicators. Through systematic analysis of tin loss characteristics, the causes of tin loss were identified. Analysis of tin loss characteristics shows that the disseminated grain size of cassiterite is mainly concentrated in the range of 5-40 μm, with the proportion of the -20 μm fraction exceeding 55%, and the dissociation degree of cassiterite is only 31.63% at the current grinding fineness. The selectivity of the three-stage series hydrocyclone desliming is poor, the metal distribution rate of +10 μm cassiterite in the desliming overflow reaches 63.62%, and the cumulative tin metal loss from the multi-stage hydrocyclone desliming operation is about 7%. Conventional mechanical agitation flotation machines have insufficient recovery efficiency for -10 μm ultra-fine cassiterite. Technical renovation tests were carried out to break through the technical bottleneck of efficient recovery of micro-fine cassiterite. The results show that by replacing the vertical stirred mill with an IsaMill for fine grinding, the content of the -38 μm fraction increases from 50% to 75%, and the dissociation degree of cassiterite increases from 46.37% to 84.21%. By replacing the three-stage hydrocyclone with a decanter centrifuge for one-stage desliming, the tin recovery rate in the underflow increases by 8.39 percentage points. By applying a microbubble flotation column to replace the conventional mechanical agitation flotation machine, along with simplifying the flowsheet structure, the tin recovery rate is increased by 7.98 percentage points compared with on-site production. Simultaneously, the flotation reagent regime is optimized by adopting the combined collectors YK-Sn, Sn-705, and Sn-F, which increases the recovery rate of the tin rougher concentrate by 6.03 percentage points compared with the original collectors. Through the systematic integration of fine grinding, high-efficiency desliming, enhanced flotation and reagent optimization, the problem of micro-fine cassiterite recovery can be effectively solved, and the pilot combined flowsheet has achieved good recovery results. The research results can provide a reference technical route for the efficient recovery of micro-fine cassiterite from similar complex polymetallic tin ores.