Abstract: The current harmonic feature and the disturbance attenuation capability of grid-tied inverter output current would be vital to power quality and system stability. The existing research focuses on the disturbance and suppression of higher-order integer harmonics, but the influence of inter-harmonics around the fundamental frequency has not been clarified. Under the condition of perturbation, the special phenomenon of grid-tied inverter, i.e., "harmonic amplification" was discovered based on the phase-locked loop (PLL) error function and the quantitative analysis of the current. The harmonic amplification characteristic frequency and the boundary of grid-tied inverter were given by theoretical analysis based on the total harmonic distortion (THD), which enriches the numerical calculation theory of inverter. Combined with the case of impedance calculation and impedance remodeling of the inverter, the practical application method of harmonic amplification mechanism was also introduced. The experimental results proved the correctness and feasibility of the theoretical analysis. The results of this paper provide a new theoretical direction and engineering design reference for perturbation suppression of grid-tied inverters.