This paper studies the modeling and interaction of the multi-VSCs(VSC, voltage source converter) system connected to the weak grid. To start with, the small-signal model of the multi-VSCs in DC voltage timescale in the weak grid is established based on the dynamic characteristics analysis method. Self-impact components and interaction-impact components are proposed to define the interaction between multi-VSCs. Furthermore, by studying the self-impact and interaction-impact components of each VSC with varied grid strengths, phase-locked loop bandwidths and terminal voltage control bandwidths, the influence mechanism of control systems on the interaction among VSCs is revealed out. Finally, detailed time-domain simulation and semi-physical models are built in Matlab/Simulink and Starsim respectively to verify the results of the multi-VSCs interaction analysis.