The invention provides a method for judging mechanical strength of a post porcelain insulator, used in the field of power equipment detection. In the method provided by the invention, the characteristic vibration frequency of the post porcelain insulator of a specified type is obtained based on vibration detection data of at least 50 post porcelain insulators with a specified type, and then, a vibration frequency region corresponding to a characteristic vibration frequency normal region and the ruled residual strength ratio is calculated according to the vibration acoustical principle. The mechanical strength of the post porcelain insulator is judged by comparing the detection data and the frequency region.