Abstract: With the increasing application of grid-forming（GFM） converters in the microgrid,the effects of GFM converters on the transient stability of the microgrid have received extensive attentions.Different from the single-machine infinite bus system,the frequency and power angle of the islanded system with parallel GFM converters are coupled with each other,and the transient response characteristics are more complex.In order to accurately analyze the transient response of the islanded system with parallel GFM converters,this paper establishes a three-order transient synchronization model of frequency and power angle difference of two GFM converters based on the power angle coupling equation of motion,and analyzes the characteristics of the influence of the power output difference and droop coefficients of two GFM converters on the transient stability.In order to reveal the coupling mechanism of power output and droop coefficient on transient stability,the equivalent synchronous power of parallel GFM converters is analyzed.An adaptive droop coefficient optimization strategy is also proposed based on the power output of GFM converters,which can adaptively increase the equivalent synchronous power of the parallel system and thus improve the transient stability of the system.Finally,the real-time simulation is used to verify the correctness of the three-order transient model and the effectiveness of the proposed control strategy.