Abstract: For efficient and direct prospecting for concealed orebodies beneath and near the exploratory well of iron polymetallic orefield in Xiaoshuigou area, Qinghai Province, the method of three-component magnetic survey in borehole is applied to study the logging data of ΔZ and ΔH' curves and change rules of ΔT' vector. It can scientifically reduce the borehole number, guide the drilling direction, accurately predict the concealed orebody around the drilling hole, and effectively improve the percentage of ore discovery.