The invention provides a vibration mode parameter identification method based on a state observer, belongs to the field of vibration mode analysis, and relates to the vibration mode parameter identification method based on the state observer. The method aims at a specific structure and a concerned vibration order, firstly an ANSTS mode is used for analysis, the vibration frequencies and vibration modes of all orders are approximately obtained, then a free vibration experiment is established, a plurality of non-contact high-resolution laser displacement sensors are adopted to measure structure displacement signals, and a mode state space equation and a state observer of the whole system are built. After the state observer is adopted to obtain free vibration mode coordinates of all orders, an FIR filter is adopted to filter out interference signals. Finally, the sinusoidal function with exponential attenuation is adopted to fit filtered mode coordinates, and the precise frequency and damping ratio of vibration of all orders are obtained. The vibration mode parameter identification method is easy to achieve, accurate in identification, high in universality, and suitable for vibration mode parameter identification of various structures.