The　space　debris　occupies　the　orbit　resources　greatly,　which　seriously　threats　the　safety　of　spacecraft　for　its　high　risks　of　collisions.　Many　theories　about　space　debris　removal　have　been　put　forward　in　recent　years.　The　Electro　Dynamic　Tether　(EDT),　which　can　be　deployed　under　gravity　gradient,　is　considered　to　be　an　effective　method　to　remove　debris　in　low　orbit　for　its　low　power　consumption.　However,　in　order　to　generate　sufficient　Lorentz　force,　the　EDT　needs　to　be　deployed　to　several　kilometers,　which　increases　the　risks　of　tangling　and　the　instability　of　the　EDT　system.　In　the　deployment　process,　different　initial　in-plane/out-of-plane　angles,　caused　by　direction　error　at　initial　release　or　the　initial　selection　of　ejection,　affect　the　motion　of　EDT　system　seriously.　In　order　to　solve　these　problems,　firstly,　this　paper　establishes　the　dynamic　model　of　the　EDT　system.　Then,　based　on　the　model,　safety　metrics　of　avoiding　tangling　and　assessing　system　stability　during　EDT　deployment　stage　are　designed　to　quantitatively　evaluate　the　EDT　system　security.　Finally,　several　numerical　simulations　are　established　to　determine　the　safety　ranges　of　the　initial　in-plane/out-of-plane　angles　on　the　EDT　deployment.　(C)　2020　Chinese　Society　of　Aeronautics　and　Astronautics.　Production　and　hosting　by　Elsevier　Ltd.　This　is　an　open　access　article　under　the　CC　BY-NC-ND　license　(http://creativecommons.org/licenses/by-nc-nd/4.0/).