The transient synchronous stability issue of voltage source converters is a typical nonlinear problem, which especially exhibits complex higher-order and interacting coupling characteristics in multi-converter systems. To clarify the interactive coupling characteristics and transient instability mechanism of the heterogeneous system with multiple control mode converters, a dual- converter hybrid grid-connected system consisting of grid-following voltage source converter （GFL-VSC） and grid-forming voltage source converter （GFM-VSC） is studied. Firstly, the mathematical modeling of the hybrid parallel system for transient stability analysis is developed using phasor analysis, and the mechanism of interactive coupling between two inverters is revealed. Then, by introducing three-dimensional surfaces and contour lines, a visual stability analysis method is proposed, which can intuitively describe the system balance relationship. Furthermore, the effects of the active power reference and reactive power control circuit of GFM-VSC and the current reference of GFL-VSC on transient stability are revealed in detail. The results show that the reactive power control introduction of GFM-VSC deteriorates the system balance relationship. The stability of the system can be improved by decreasing the active current injection of GFL-VSC and increasing its reactive current injection, or by decreasing the active power reference of GFM-VSC during grid faults. Finally, the hardware-in-the-loop experiments verify the correctness of the theoretical analysis.