The　development　of　urban　underground　space　can　increase　the　green　area　of　a　city　and　have　a　positive　impact　on　urban　microclimate.　However,　the　negative　impacts　of　urban　under-ground　space　development　on　the　urban　microclimate　are　rarely　considered　and　analyzed.　In　this　study,　we　focus　on　analyzing　the　impact　of　the　development　of　underground　commercial　streets　under　determinant　urban　form　on　urban　microclimate　using　outdoor　CO　concentrations　as　the　evaluation　index.　In　this　regard,　it　was　possible　to　quantitatively　evaluate　the　influences　of　various　development　factors　(e.g.,　development　intensity　of　underground　commercial　streets;　location　and　height　of　shaft　exhaust;　and　various　ground-greening　configurations　of　transverse　and　vertical　trees,　large　and　small　shrubs,　and　grasses)　on　the　outdoor　CO　concentration.　The　results　showed　that　higher　development　intensity　increases　outdoor　CO　concentration　and　its　range　of　effects.　Properly　increasing　the　height　of　shaft　exhausts,　choosing　a　dispersed　layout　for　shaft　exhausts,　and　planting　large　shrubs　on　the　ground　in　the　development　area　of　underground　commercial　streets　can　effectively　reduce　the　impact　of　underground　commercial　street　development　on　urban　air　quality.