The　major　objective　of　this　work　is　to　investigate　the　Joule-Thomson　effect　(J-T　effect)　of　CO2　leakage　through　vertical　porous　pathways.　A　one-dimensional　depressurization　process　model　is　established,　in　which　the　Span-Wagner　equation　is　employed　to　describe　the　thermophysical　properties　of　CO2.　The　effects　of　heat　exchange　between　CO2　and　the　surroundings,　pressure　drop,　and　the　permeability　of　leaky　pathways　on　the　J-T　effect　are　presented　for　different　leakage　scenarios.　The　results　indicate　that　a　large　temperature　drop　is　present　along　the　leaky　pathway　due　to　the　drastical　variation　of　the　thermophysical　properties　of　CO2.　Based　on　the　hierarchical　leakage　scenarios,　the　J-T　effect　always　leads　to　the　CO2　temperature　profile　approaching　the　CO2　saturation　line,　whereas　the　heat　exchange　between　CO2　and　the　surroundings　induces　the　CO2　temperature　profile　inclining　to　the　geothermal　temperature　distribution.　A　remarkable　temperature　drop　is　observed　due　to　the　larger　pressure　drop,　although　the　increase　in　the　permeability　of　the　leaky　pathway　mitigates　the　influence　of　heat　transfer　on　the　J-T　effect.　For　the　direct　leakage　scenario,　a　sharp　temperature　drop　of　CO2　appears　in　the　near-surface　segment.　The　inlet　depth　of　the　leaky　pathway　primarily　determines　the　pressure　drop,　the　temperature　drop,　and　the　flow　rate　of　CO2　leakage.　For　different　scenarios　of　CO2　leakage,　an　in-depth　data　analysis　of　the　CO2　depressurization　process　will　provide　insight　into　the　monitoring　and　evaluation　of　CO2　leakage.