Recovering C 2 H 4 from refinery gas is an effective way to broaden the source of ethylene. However, it's a challenging task to separate C 2 H 4 and C 2 H 6 due to their very close physical properties and molecular size. Metal-organic frameworks (MOFs) are shown broad prospects in the field of light hydrocarbon separation in recent years. In this work, NH 3 is used to modify the structure of UTSA-280, the efficient separation of C 2 H 4 /C 2 H 6 can be achieved through the adjustment of one-dimensional channels. UTSA-280 has undergone stepwise adsorption of ammonia gas at 298 K and 100 kPa. After partial ammonia removal, we obtained the modified UTSA-280 that ammonia adsorption modification with a mass loading of 5.6% for UTSA-280-M1 and 2.8% for UTSA-280-M2. The NH 3 modified UTSA-280 shows a unique ultramicroporous structure that can enhance the adsorption of C 2 H 4 and does not adsorb the slightly larger C 2 H 6 , achieving the ideal C 2 H 4 /C 2 H 6 adsorption selectivity (more than 1000). Ammonia molecules play the role of perfectly adjusting the size of one-dimensional channels and realize the ideal screening effect of C 2 H 4 /C 2 H 6 . The C 2 H 4 adsorption capacity of NH 3 modified UTSA-280-M2 can be improved to 2.83 mmol/g at 298 K and 100 kPa (an increase of 29% compared with initial material). And its ultramicroporous structure can fully block the adsorption of C 2 H 6 , which finally achieves a C 2 H 4 /C 2 H 6 selectivity over 1200. Grand Canonical Monte Carlo (GCMC) simulation of C 2 H 4 /C 2 H 6 mixed gases (equal volume) adsorption results showed that the modified UTSA-280 had more C 2 H 4 adsorption distribution in the mixed components than C 2 H 6 . Through the C 2 H 4 /C 2 H 6 mixed gases breakthrough test at 298 K, NH 3 modified UTSA-280-M2 shows a separation time of more than 48 min, which is more than the initial 25 min. Compared with the unmodified material, the separation performance is nearly doubled. Scalable synthesis, stable structure, and the advantages of controllable performance after ammonia modification have prompted this material to have great prospects in the industrialization of C 2 H 4 /C 2 H 6 separation. Keywords metal-organic frameworks; NH 3 modification; C 2 H 4 /C 2 H 6 separation; selectivity