The　terrestrial　discrete-LiDAR　is　a　promising　instrument　to　obtain　the　accurate　LAI　and　PAI　estimates　of　forest　canopies　as　compared　to　the　traditional　optical　methods,　as　it　has　the　ability　of　insensitive　to　the　observation　conditions　and　recording　the　3D　structural　information　meanwhile.　In　this　paper,　the　ability　of　terrestrial　discrete-LiDAR　for　capturing　the　gap　fraction　and　retrieving　the　PAI　of　forest　canopies　were　analyzed　using　14　3D　forest　scenes　with　known　PAI.　These　estimates　from　the　LiDAR　method　was　compared　to　these　from　the　DHP　method.　The　ability　of　the　LiDAR　method　for　retrieving　the　gap　fraction　and　PAI　of　forest　canopies　was　discussed　and　concluded　in　the　end.