A crystal oscillator, comprising: a crystal; an oscillating circuit comprising a first oscillating transistor and a second oscillating transistor, wherein the first oscillating transistor and the second oscillating transistor are configured to provide transconductance for starting oscillation and maintaining oscillation of the crystal; a first driving circuit configured to generate a stable reference current; and a second driving circuit, configured to supply an operating voltage to the oscillating circuit and make an operating current of the first oscillating transistor and the second oscillating transistor be a stable current according to the reference current, wherein the operating voltage is configured to control the first oscillating transistor and the second oscillating transistor to operate in a sub-threshold region; the second driving circuit is configured to receive the reference current generated by the first driving circuit and generates the operating voltage according to the reference current; the second driving circuit comprises a first current control transistor and a second current control transistor, and the first current control transistor and the second current control transistor are configured to control the operating current of the first oscillating transistor and the second oscillating transistor to be the stable current, and connection structures of the first current control transistor and the second current control transistor are the same as connection structures of the first oscillating transistor and the second oscillating transistor, and a ratio of sizes of the first oscillating transistor and the first current control transistor is equal to a ratio of sizes of the second oscillating transistor and the second current control transistor. a crystal; an oscillating circuit comprising a first oscillating transistor and a second oscillating transistor, wherein the first oscillating transistor and the second oscillating transistor are configured to provide transconductance for starting oscillation and maintaining oscillation of the crystal; a first driving circuit configured to generate a stable reference current; and a second driving circuit, configured to supply an operating voltage to the oscillating circuit and make an operating current of the first oscillating transistor and the second oscillating transistor be a stable current according to the reference current, wherein the operating voltage is configured to control the first oscillating transistor and the second oscillating transistor to operate in a sub-threshold region; the second driving circuit is configured to receive the reference current generated by the first driving circuit and generates the operating voltage according to the reference current; the second driving circuit comprises a first current control transistor and a second current control transistor, and the first current control transistor and the second current control transistor are configured to control the operating current of the first oscillating transistor and the second oscillating transistor to be the stable current, and connection structures of the first current control transistor and the second current control transistor are the same as connection structures of the first oscillating transistor and the second oscillating transistor, and a ratio of sizes of the first oscillating transistor and the first current control transistor is equal to a ratio of sizes of the second oscillating transistor and the second current control transistor.