Grid harmonic interactions among multiple Flyback micro-inverters have been studied. The method of small-signal modeling and time-domain analysis based on transformer current equation are adopted to obtain the Norton model of Flyback micro-inverters with current feedback control in CCM mode and with quasi-resonant peak current control in BCM mode; impedance-based stability mechanism is analyzed. Based on derived Norton model and system of admittance matrix, the resonant frequency is calculated and predicted. And by comparing, it is found that quasi-resonant peak current control has better performance on damping the harmonic interactions than current feedback control. Theory analysis and simulations are carried out, two sets of 250W prototypes are designed for the experimental verification.