In　order　to　study　the　metrical　problems　in　gas　injection　wells　and　production　wells　for　the　vertical　distance　in　SAGD(steam　assisted　gravity　drainage),　the　alternating　magnetic　field　generated　in　the　fluxgate　sensor　rotary　magnetic　beacon　was　applied　to　calculation　the　distance.　Three　axis　fluxgat　sensor　output　values　were　used　to　calculate　the　vertical　distance　between　the　two　holes,　and　kept　the　distance　between　the　first　and　second　boreholes　within　a　certain　range,　thus　effectively　made　wells　keep　parallel.　In　order　to　compensate　for　the　effects　of　perturbing　magnetic　fields　associated　with　magnetized　sections　of　the　drill　collar,　a　correction　method　of　determining　the　distance　which　relied　on　the　knowledge　of　local　geomagnetic　field　and　interference　magnetic　field　was　described　in　detail.　The　measuring　experiments　show　that　the　correction　method　can　determine　an　accurate　vertical　distance　under　the　environment　of　the　disturbance　of　magnetic　material.　It　is　simple,　effective　and　practical,　and　beneficial　to　improving　the　recovery　of　oil　resources.