The tangent technique of Δ T profile magnetic anomaly is a kind of traditional effective method for calculating buried depths of magnetic plates in intermediate-high magnetic latitude areas. Based on this method, the authors put forward the "reverse tangent" technique of Δ T profile negative magnetic anomaly for calculating buried depths of magnetic plates in low magnetic latitude areas, and demonstrate its theoretic correctness. By means of such a "reverse tangent" technique, the traditional tangent technique of Δ T profile magnetic anomaly and its coefficient tables in the intermediate-high magnetic latitude area can be directly used to calculate the buried depth of the magnetic plate which usually produces Δ T profile negative magnetic anomaly in the low magnetic latitude area.