To ensure that a hardware Trojan remains hidden in a circuit, it is usually necessary to ensure that the trigger signal has a low testability, which has been widely recognized and proven. The most advanced testability-based detection methods are rather slow for large circuits, and the false-positive rate is not as low as that for small circuits. In this paper, a hardware Trojan, through the low testability of the trigger signal and its position characteristics in the circuit, was detected, which greatly improves the detection speed while maintaining a lower false positive rate when being applied to large circuits. First, the Sandia Controllability/Observability Analysis Program (SCOAP) was applied to obtain the 0–1 controllability of the signals in the netlist. Secondly, the controllability value was calculated by the differential amplification model, in order to facilitate K-means clustering to get better results. Then, we calculate the shortest path between each suspicious signal to get the connection between each suspicious signal. Finally, we divide the suspicious signals into several suspicious circuit blocks to screen the real trigger signal. As a result, the false-negative rate of 0% and the highest false-positive rate of 5.02% were obtained on the Trust-Hub benchmarks.