Manufacturing method of mixed signal integrated circuit

The invention provides a manufacturing method of a mixed signal integrated circuit. The manufacturing method comprises the following steps of according to a preset first process flow, forming a grid of a MOS (metal oxide semiconductor) tube, a polycrystalline high resistor and a lower electrode plate of a double-polycrystalline capacitor on a first polysilicon layer; according to a preset second process flow, forming an upper electrode plate of the double-polycrystalline capacitor on a second polysilicon layer; according to a preset third process flow, forming a source and drain area of the MOS tube. The manufacturing method has the advantages that the polycrystalline high resistor is formed on the first polysilicon layer, the source and drain area of the MOS tube is formed after the polycrystalline high resistor, and the high-temperature process is needed in the forming process of the source and drain area of the MOS tube and other process steps, so the ion doping in the polycrystalline resistor is fully activated, and the accuracy of the polycrystalline high resistor is improved.