The　drift　of　particle　guiding　centre　in　inhomogeneous　magnetic　field　is　discussed　by　making　use　of　the　average　magnetic　force　on　an　equivalent　circular　current　loop,　and　a　model　for　Larmor　gyration　of　a　charged　particle.　Consequently　two　drift　speed　components　perpendicular　to　the　magnetic　field　is　presented　through　the　way　of　three-dimensional　vector　arithmetic,　including　the　familiar　term　of　grad　B　drift　and　an　extra　drift　term　caused　by　∇　×　B,　which　will　be　helpful　to　realize　the　drift　instability　of　the　high　temperature　fusion　in　magnetic　confinement.