On-chip　spiral　inductors　with　high　quality　factors　are　very　important　in　many　RF　circuits.　In　this　paper,　spiral　inductors　are　analyzed　to　study　the　influence　of　substrate　and　spiral　structure　on　an　inductor＇s　performance　in　the　multi-GHz　frequency　range.　Firstly,　the　inductors　with　different　substrate　conductivity,　thickness　and　permittivity　of　the　dielectric　layer　are　compared,　and　a　general　guide　is　given　that　the　substrate　of　a　good　performance　inductor　should　be　light　impurity,　the　dielectric　layer　should　be　thick,　and　use　a　low　k　material.　And　then,　this　paper　presents　a　novel　spiral　structure　with　gradually　reduced　metal　width　and　space　from　outside　to　inside,　which　can　help　to　alleviate　the　problems　of　the　magnetic　field　intensity　of　a　spiral　inductor　increasing　gradually　from　outside　to　inside.　Compared　to　conventional　inductor,　the　maximum　Q　of　inductor　using　gradually　changed　structure　increases　by　13.66%,　thus　the　results　have　corroborated　the　validity　of　the　proposed　method.　©2009　IEEE.