This paper discusses the response of central-loop TEM in relation to various working parameters with forward modeling procedure. The discussing results will be helpful for choice of working parameters and interpretation of TEM data. There are two results gotten from the discussing. First, when considering homogeneous conductive half-space, the radius of the transmitting circle loop is larger, the response attenuation is slower and the early time is longer. The early response is influenced more seriously than the late response by ramp time. the effect of ramp time is to decrease the response. Second, when considering half conductive space containing a lowly or highly conductive target layer, though the radius of the transmitting circle loop is various, the time scope of the anomaly caused by target layer is same. With increase of the radius, the anomaly moves from the early time to the late time. The relative anomaly of highly conductive layer is negative in the early time, positive in the late time. The relative anomaly of lowly conductive layer is positive in the early time, negative in the late time. The relative anomaly of target layer is larger in the late time than the early time. It's influenced seriously in the early time, decrease with increase of the ramp time. But if it's in the late time, decreases slightly with increase of the ramp time. So when the transmitting circle loop is chosen, it should be considered letting the anomaly caused by target layer locate in the late time.
