Abstract: Under the background of high proportion of new energy connected to the power system, the number of grid connected converters deployed in the distribution network is increasing, and the secondary harmonic generated by the nonlinear characteristics of grid connected converters has gradually become one of the important sources of harmonic pollution in the distribution grid. Therefore, the secondary harmonic components of the sideband generated from A/D sampling and PWM modulation of grid connected converters are studied. The generation and frequency coupling mechanisms of the secondary harmonic components of the sampling and PWM sideband are analyzed. The analysis method of PWM sideband harmonics under different sampling methods is presented. The quantitative analysis model of the secondary harmonic components of grid connected converters sampling and PWM sideband is established. The main factors affecting the secondary harmonic content of the sideband are analyzed. The influence of sideband secondary harmonic coupling effect on the impedance characteristics of grid connected converter is proposed. The accuracy of the theoretical analysis is verified by the test results of the hardware in the loop simulation platform.