The present application provides a TFT, a manufacturing method thereof, and a sensor. The TFT includes a substrate, and a source, a drain and an active layer on the substrate. The active layer includes a microchannel, and the thin film transistor is configured to detect a sample in the microchannel. When a sample to be detected enters the microchannel, the electron distribution in the active layer would be affected, which causes fluctuations in the TFT characteristics. By detecting such fluctuations, detecting the composition and property of the liquid to be detected may be achieved. Moreover, by virtue of the microchannel, the sample may be precisely controlled. The impact of the external environment may be reduced and the detection accuracy can be enhanced. Continuous monitoring instead of one-time detection of the sample may be achieved and the sample detection efficiency may be improved.