Airborne time-domain electromagnetic(ATEM)system has some advantages, such as high-speed, economy and deep-exploration depth. ATEM is one of effective methods to explore water resources and minerals. Study on the detection resolution of three-dimensional (3-D) geological body has great importance in ATEM detection in China. The article using finite-difference time-domain method (FDTD) and Central loop mode calculates the airborne electromagnetic response of 3-D typical geologic body. We had discussed the detection resolution of 3-D targets which were in different depth or electrical conductance. Combine with the reality operating parameters of ATEM system, and we calculated 3-D anomalous body of 70 m?70 m?70 m. Numerical calculation results indicate that, when the ratio of electrical conductance of abnormal and background is 200, the maximum range of detecting depth is 180 meters. When reasonable improve the magnification of the receiver front-end, you can effectively enhance the exploration depth. When anomalous body is buried 135m depth, can detect the minimum ratio of electrical conductivity of anomalous body and the surrounding rock is 1.5. Using ATEM methods to study 3-D anomalous body's resolution has great guiding significance of the theory in recognition of anomaly and precise processing for electromagnetic data interpretation.