Abstract: The grid-forming (GFM) energy storage system (ESS) is regarded as the key equipment for building a new-type power system because of its ability to solve new energy consumption and improve the rotational inertia of the system. This paper focuses on the influence of GFM-ESS access on the grid-connected stability of new energy power stations. First, the modeling and frequency characteristics of GFM-ESS and grid-following energy storage system (GFL-ESS) are presented, and the influence of GFM-ESS and GFL-ESS on the grid-connected system stability is analyzed. The results show that the GFM-ESS is more conducive to improving the grid-connected system stability. On this basis, the influence of the GFM-ESS on the impedance characteristics of the new energy power station is explored. In view of the prominent negative resistance characteristics of the new energy unit in the weak dominant frequency band, an autonomous impedance adaptive control is proposed to improve the impedance dominant ability of the GFM-ESS. Based on the real-time detection of the system resonance frequency, the autonomous impedance adaptation with different grid conditions is realized, the GFM-ESS can effectively improve the grid-connected system stability. Finally, the experimental verification of the relevant frequency characteristics and the effectiveness of the autonomous impedance adaptation control method are depicted by the hardware-in-the-loop platform.