The average-current-controlled boost power factor correction converter may operate in all-continuous current mode (CCM), part-CCM/discontinuous current mode (DCM), or all-DCM mode in a half line cycle under different input voltage and load conditions, and the conducted electromagnetic interference (EMI) spectrum of the converter exhibits differences in these operation modes. In this paper, by analyzing the characteristic of the harmonics of the drain-to-source voltage of the power switch, the characteristics of the common-mode and differential-mode noise of the converter are revealed in different operation modes. The analyzed results can be used to guide the EMI filter design for the converter and ensure the conducted EMI satisfying the standard under all working conditions.