The invention discloses a FET (Field Effect Transistor) bias circuit, including current changing information circuit that has a power source resistance connected with the signal output end of this circuit, the other end of the resistance is connected with a reference voltage source, and the node between the resistance and the current changing information circuit acts as the output end providing the voltage changing information; and a voltage divider circuit connected with at least one voltage source, the voltage divider circuit is connected with the output end providing the voltage changing information; the current in a signal action FET is controlled by providing the voltage changing information at the output end to the voltage divider circuit and getting a dividing voltage from the voltage divider circuit to be a output end of the FET bias circuit. The bias circuit of the invention can make the static drain current of the signal action FET to remain constant, and reduce the deviation of the static drain current of the signal action FET of each chip in the whole wafer and its cost is low, its area is small, and it is easy to be integrated and fabricated.