Due to the self-transition of the loop, the early signal of TEM suffers great distortion. In order to study characteristics of the early signal with TEM, the authors formulated self-induction formulae for single coil and multi-turn coils, deduced theoretical expressions for the amplitude of the loop self-induction signal, and gave the induction of single coil and multi-axial coils. The response curve of buried object affected by the coils and the length of loop's change are also studied. The results obtained lay a foundation for further studies of the additional effect of the early field and can serve as reference data for further researches.