Supraharmonics are a new power quality problem that can not be ignored in new energy power generation technology. As a typical supraharmonic source,the grid-connected inverter has received extensive attentions. To reveal the characteristics of its generation and propagation mechanism,the mechanism of supraharmonic generation in sinusoidal pulse width modulation (SPWM) inverters is analyzed firstly. It is found that the supraharmonics generated are mainly distributed around integer multiples of the switching frequency,and can be equivalent to a voltage source. At the same time,the influencing factors that cause changes in the voltage source are theoretically analyzed. Then,a supraharmonic circuit model including inverter,filter and grid side impedance is established,and the mathematical expression of supraharmonic emission current is derived. On this basis,the influence of capacity and number of inverters on supraharmonic propagation characteristics when multiple inverters are connected in parallel is explored through the control variates. Finally,the simulation experiment is carried out in Simulink. The results show that supraharmonics in the grid-connected inverter are mainly affected by the DC side voltage and modulation ratio,and the emission intensity of supraharmonics is proportional to the capacity when multiple inverters operate in parallel. The correctness of the theoretical analysis of supraharmonics in the grid-connected inverter is verified in this paper.