a constant current generating circuit and constant current generating method applied to a chip are provided , where the chip includes a first current generating circuit and a second current generating circuit , the second current generating circuit includes a transistor and an adjustable resistor . the constant current generating method includes : connecting an external resistor to the first current generating circuit to make the first current generating circuit use the external resistor to generate a first current ; utilizing the second current generating circuit to generate a second current ; adjusting the adjustable resistor in accordance with the first current and the second current to make the second current substantially equal to the first current , where the second current serves as a constant current of the chip .