In Nanpu oilfield, dense cluster wells are with high drilling density, small wellhead spacing, large development time span of the same platform, and dense intersecting of new and old wellbore trajectories. The problem of drilling collision prevention is prominent, especially the track spacing of upper well sections is small, and magnetic interference often exists in the actual drilling process. The conventional anti-collision scanning calculation method is insufficient and can not fully meet the needs of safe drilling of dense wells. According to the geometric relationship between positive drilling and adjacent well trajectory at collision prevention point, the concept of out-of-plane angle of well trajectory is put forward. Through theanalysis of the out-of-plane angle, the spatial relationship between the positive well and the adjacent well can be judged. On the basis of analyzing the sensing distance of the measuring tool to the casing magnetic field and the distance from the measuring point to the drill bit, the concept of the cut-in angle is proposed. According to the small spacing of MWD magnetic interference, the distance between the measuring point and the drill bit, and the spatial relationship of the borehole trajectory, two anti-collision relationships under the state of magnetic interference are summarized, and the drilling anti-collision judgment and control method are established. Field examples prove that this method enriches the methods of anti-collision and control of drilling under the condition of small spacing magnetic interference in the upper sections of dense cluster wells.