Selective production of specific products, such as jet fuel, in Fischer–Tropsch synthesis (FTS) is a huge challenge due to the Anderson–Schulz–Flory (ASF) distribution law. Herein, by filling K-promoted Fe-based active species, which usually produces medium-to-short chain hydrocarbons in high-temperature FTS, into the hierarchical carbon nanocages (hCNC), jet fuel with high selectivity of 60% is directly obtained in FTS at 300 °C, exceeding the ASF maximum limitation of ca. 41%. Through the theoretical simulations, we attribute this performance to the CO enrichment inside the nanocavities due to the sieving effect of the micropores across the hCNC shells (~ 6 Å) and the increased collision frequency in confined space. These two factors thereby promote the CO conversion and carbon-chain growth longer over the catalytically active Fe₅C₂ phase, resulting in the remarkable selectivity to jet fuel. The effects of the length and size of micropores on the CO/H₂ diffusion and FTS performance are examined, which corroborate the crucial role of micropores in the high-selective FTS to jet fuel. This work not only provides a remarkable catalyst to the selective jet fuel synthesis, but also offers an alternative way to design advanced catalysts for FTS.