The principle of airborne time domain electromagnetic system is that Tx coil transmits electromagnetic pulse into ground, and Rx coil receives the induced secondary EM fields from conductive bodies in the earth. The secondary fields generated by induced current of conductive bodies contain geological information. Data processing and interpretation help to achieve prospecting for multi-metal mineral resources. The authors analyzed features of time constant reflection to power line interference under the conditions of near surface conductive bodies, near surface weak conductive bodies, and deep conductive bodies respectively and summarized the characteristics of time constant of different geological bodies based on knowledge of known mineral formation and two years' experience in airborne EM surveys. Some conclusions have been reached: the power line interference generally shows a discontinuous linear anomaly in τ map and electromagnetic response is jumping like irregular attenuation; low resistivity anomaly generally shows high value area in τ map and the electromagnetic response decays exponentially. The low resistance body decays more slowly when the conduction is better and the body is bigger.