Abstract: Based on a physical model developed to present the development of the lower and mid-latitudes spread-F, the effects of different disturbances of electron density on triggering spread-F are compared and the evolution of plasma bubble and blob irregularities under different perturbation wavelengths of electron density are discussed.The results show that no matter electron density is bubble or blob structure, the disturbances with short wavelength are much easier to trigger spread-F than long ones.When the initial disturbance with decreasing electron density exists in one side and increasing electron density disturbance appears in another side at the same time, the perturbation amplitude of each other will be much more enhanced than that when they appear respectively, and the uplift rate of bubble structure is much faster than blob. Even if at the same level of electron density, the electron density bubble and blob structure do not always be lifted or developed simultaneously and they do not always keep the same tendency.