The broadband harmonic components such as background harmonics of the distribution network and the the switching harmonics from the power electronic equipments operating in parallel can inject into the power electronic converter control system by voltage and current sampling. These harmonics can be transmitted to the pulse width modulation (PWM) stage. Under the influence of the sideband effects, a series of secondary sideband harmonics related to disturbance harmonic frequency will be generated in the PWM output waveforms, which exacerbate the harmonic distortion of power electronic converters and become important sources of harmonic pollution in power electronic distribution networks.Therefore, PWM sideband harmonic analysis models considering the influence of wideband background harmonic disturbance were established for five typical PWM modulation methods and simulated for verification. An improved Total Harmonic Distortion (ITHD) evaluation index suitable for PWM harmonic performance analysis under broadband background disturbances is proposed; Finally, based on the mathematical model and the proposed ITHD index, the influence of sampling methods, carrier forms and amplitude of background harmonic on the sideband harmonic emission characteristics was analyzed.