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.