A voltage source circuit for a crystal oscillation circuit is provided, in which the voltage source circuit and the crystal oscillation circuit are formed with the same process. The voltage source circuit includes a current source, a first PMOS, a first NMOS and a regulator unit. The current source is coupled between a voltage source and an output terminal, in which the output terminal outputs a reference voltage. Both of the gates and drains of the first PMOS and the NMOS are coupled to each other, and the first PMOS and the first NMOS are coupled between the output terminal and a ground. The regulator unit generates a work voltage to the crystal oscillation circuit as a voltage source of the crystal oscillation circuit according to the reference voltage.