Power system oscillation instability is a serious threat to the safe and stable operation of a power system. Driven by the "double carbon" goal and energy transformation, large-scale wind power grid connection has aggravated the oscillation stability problem of the new power system. In this paper, an accurate synthesis model of a doubly fed wind power grid connected system is established by considering all parts of the power system such as the drive system, wind turbine converter, phase-locked loop and series compensation. Then, based on the mode analysis method, the relationship between the system oscillation mode and the participation factors is analyzed. The strongly related state variables and dominant factors that cause the system oscillation mode are determined, and the broadband oscillation mechanism of the doubly fed wind power grid-connected power system is explored. The oscillation suppression method is found. To compare with the traditional model, simulation and verification are carried out on the Matlab software platform. The results show that the model and mechanism analysis method established represent more abundant oscillation mode information with more state variables, explain the system wide-band oscillation mechanism in more detail, and eliminate the oscillation, improving system damping and stability. It lays a theoretical foundation for further research and development of power system wide-band oscillation detection and suppression methods.