A fast bias circuit including a bias unit, a resistor, a first switch, and a detecting circuit is provided. The resistor has a first terminal coupled to the bias unit to receive a bias voltage, and a second terminal coupled to a bias terminal of a target circuit, wherein the bias terminal is coupled to an input signal. The first switch has a first terminal coupled to the first terminal of the resistor, a second terminal coupled to the second terminal of the resistor, and a control terminal coupled to the detecting circuit. During an initialisation period, the detecting circuit compares the bias voltage with a voltage at the bias terminal of the target circuit to obtain a comparison result, and controls the first switch according to the comparison result. Furthermore, a fast bias method and a bias and load circuit are also provided.