In the process of drilling monitoring，when well bottom approaches the target point，rectification trajectory is generally designed with ‘line segment-arc method’. The mathematic model has been established, and analytic solutions of mathematic model are given for 4 solving combinations. One application of analytic solutions is illustrated: drawing graphics of analytic solutions can enable the user of computer software to design rectification trajectory rationally. Actual calculated cases indicated that accurate rectification trajectory could be quickly designed by analytic solutions, which has guiding significance in drilling monitoring.