A fast and efficient numerical calculation method of full-domain apparent resistivity for AGTEM has been developed in this paper. We defined the full-domain apparent resistivity using the vertical and horizontal component of time domain magnetic field, in this way we can achieve full space, all time domain apparent resistivity definition. We analyzed thoroughly the Air-ground transient electromagnetic field analytic expression in homogeneous half space, and discovered that the Air-ground time domain response can be expressed in similar polynomial with the central vertical response, use the apparent resistivity translation algorithm, we can achieve full-domain apparent resistivity definition. Model calculation results show that the apparent resistivity definition method does not require iterative, with quicker speed and higher precision. Finally, compared the magnetic field and the voltage based apparent resistivity for resolution of abnormal body.