Abstract: In the well-trajectory guidance based on the magnetic field survey, establishing the appropriate algorithm has been the research difficulty, of which the distance and deviation angle between Horizontal wells and caves is a necessary condition for connectivity. for the key of vector- Distance algorithm , Curve fitting is used for the derivation of deviation angle algorithm, demonstrating the feasibility of deviation angle Algorithm and the error analysis. Additionally, Inductive method is used for derivation of distance formula between center of mangnet sub and vertical well . Proposed the new algorithm for the bore hole path’s direction detection.