The invention discloses a structure for reducing in-band noise in a multistage power amplifier for mobile communication. The structure comprises a power amplifier chip, a plastic package material, a substrate and a radio shielding cover; the power amplifier chip is welded to the substrate, the portion among the radio shielding cover, the power amplifier chip and the substrate is filled with the plastic package material, a heat conducting material is attached to the top face of the power amplifier chip, and the radio shielding cover covers the heat conducting material and the plastic package material in an attached mode. The plastic package method includes the steps that the power amplifier chip is welded to the substrate, and the heat conducting material is attached to the top face of the power amplifier chip; the plastic package material is used for plastic filling, and the top face of the plastic package material is made to be flush with the top face of the heat conducting material on the power amplifier chip. By means of the packaging method, the radio shielding cover is used as a radiator of the power amplifier chip, the chip can radiate heat faster, heat noise of the device is reduced, and in-band noise is reduced.