For electronics products to become more miniature, the signal will much easier to be interference. Power noise is considered to be the main issue to signal interference. As stated above, Power Integrity (PI), Signal Integrity(SI) and Electromagnetic Compatibility (EMC) issues are gradually important. This paper researches interference distribution of power noise on the Printed circuit board(PCB) and analyzed its mechanism. The relationship between return path and noise interference is also proposed in this paper. With frequency domain and time domain nearfield measurement technology, the frequency band of power noise interference and mechanism of power noise interference could have a direct result for analysis.