On the Loran-C System, the systematic errors of the time differences depend on the conditions of the propagated paths. These conditions decided for conductivities and irreguralities of terrains induce a phase and envelope distortion on these pulse signals, and these distortions are difficult to predict. On this point of view, in this paper, it is shown that the bias errors of the time difference measurements were almost eliminated utilizing the Envelope-to-Cycle Difference measurements and model under ideal land conditions.