Abstract: In the virtual synchronized power grid, the inertia difference among devices is obvious, and the multi-scale characteristics are prominent, which cannot be handled well by traditional simulation methods. This paper proposes a simulation method based on Haar wavelet collocation method for dynamic simulation of virtual synchronized power grid system. First, multi-scale characteristics of the virtual synchronized power grid are revealed and limitations of traditional simulation methods in multi-scale system simulation are analyzed. Then, basic knowledge of wavelet collocation method is introduced to establish the wavelet-form multi-scale simulation model for the virtual synchronized power grid, which is then solved by the Haar wavelet collocation method by constructing the interpolation points within integration steps. Moreover, time complexity and cumulative error of the method are analyzed. In order to improve the simulation efficiency, a multi-level and multi-interval adaptation simulation strategy is further proposed, and the calculation process for the optimized Haar wavelet collocation dynamic simulation is provided. Finally, using virtual synchronized power grids of different scales, the proposed method is compared with traditional commercial simulation algorithms. Results show that the proposed method is accurate and reliable with high-order precision and fast simulation speed, which can realize large-step simulations for the multi-scale virtual synchronized power grid.