Ammonia,　as　an　efficient　hydrogen　storage　carrier,　has　great　potential　to　replace　fossil　fuel　energy.　The　use　of　refined　oil　pipelines　to　increase　the　infusion　of　liquid　ammonia　can　make　full　use　of　the　pipeline　capacity　and　save　transportation　costs.　The　phase　equilibrium　problem　of　the　liquid　ammonia-refined　oil　blend　system　is　of　great　significance　to　the　pipeline　transportation　process,　and　the　decompression　process　will　cause　more　complex　phase　change　problems.　In　this　paper,　the　effects　of　ammonia/oil　ratio　and　moisture　content　on　the　phase　equilibrium　and　decompression　phase　change　of　the　liquid　ammonia-refined　oil　mixed　system　were　clarified,　the　phase　equilibrium　pressure　of　the　liquid　ammonia-refined　oil　mixed　system　was　obtained,　and　the　phase　change　mechanism　of　the　liquid　ammonia-refined　oil　mixed　system　was　revealed.　It　is　found　that　the　equilibrium　vapor　pressure　of　the　ammonia-oil　mixed　system　is　less　than　the　saturation　vapor　pressure　of　the　two　pure　components　in　0—30℃,　and　is　greater　than　the　saturation　vapor　pressure　of　pure　liquid　ammonia　in　−2—0℃,　and　reaches　the　maximum　value　when　the　oil　volume　ratio　is　0.3.　At　the　same　time,　the　presence　of　moisture　reduces　the　equilibrium　vapor　pressure　of　the　ammonia-oil　mixture.　The　ammonia-oil　anhydrous　mixed　system　will　produce　bubbles　during　the　decompression　process.　The　lower　the　pressure,　the　more　bubbles　there　are,　and　the　more　intense　the　foaming　behavior.　The　aqueous　liquid　ammonia-oil　mixing　system　generates　droplet　clusters　during　decompression,　which　slowly　become　larger　and　aggregate,　and　form　large　droplets　that　remain　at　the　bottom　at　the　end　of　decompression.　The　above　research　results　have　important　theoretical　guiding　significance　for　the　development　and　application　of　ammonia　infusion　technology　in　refined　oil　pipelines.　©　2025　Materials　China.　All　rights　reserved.