The doubly-fed induction generator (DFIG) wind power system based on virtual synchronous generator (VSG) has been widely concerned because of its advantages of providing virtual inertia support and self-synchronizing voltage source characteristics. In order to analyze the small-signal stability performance, this paper establishes a VSG based overall system model. For the algebraic equation calculation and cancelation of the PCC among the grid, DFIG stator and grid-side converter, there are some problems such as complex calculation process, mathematical model mismatch, and unclear physical meaning, so the doubly-fed machine model based on the Thevenin-Norton equivalent theorem is proposed. Finally, the overall system simulation is presented and the results indicate that the system exists three oscillation modes. The ‘borrow damping phenomena’ between PLL and VSG related oscillation mode under the weak grid is found and cause system instability. This modeling method provides a theoretical basis and practical tools for small-signal stability analysis of the VSG-DFIG wind power generation system.