Abstract: The ionosphere is composed of electrostatic equilibrium plasma, which can produce electromagnetic wave reflection, scattering, absorption and refraction, and is the key factor affecting the propagation of electromagnetic wave in the atmosphere. The delay of electromagnetic wave signal caused by the ionosphere anomaly has become the maximum error source of GPS. Ground radioactivity can cause the change of earth’s surface electric field, earth’s surface electric field change can cause the disturbance of ionosphere when the conditions of area and amplitude reach certain threshold. The main sources of ground radioactivity are cosmic rays, the decay of radioactive minerals in earth’s crust and artificial nuclear activities, among which the crustal radioactive minerals are considered as the chief source of earth’s surface atmospheric ionization. For the interpretation of the ionospheric disturbance before large earthquake, it is stated that caused by the process of earthquake preparation, the change of fault stress leads to radon gas in rock emitted from inner to surface, and then radon concentration above the fault appears abnormal. Radon progeny radioactive decay releases a lot of energy and high energy alpha particles, and then the air is ionized, which triggers a series of physical and chemical changes. A large number of ions and ion clusters are generated near the earth’s surface, forming low altitude current and local electric field, changing the atmospheric conductivity, disturbing the gradient of atmospheric electric field, causing abnormal changes of atmospheric electric field, especially in the vertical electric field, and then affecting the ionosphere. The ionosphere can be divided into D, E and F layers due to the obvious stratification of its electron density. In order to simplify the analysis model, the single-layer model was adopted as the structure model of the ionosphere for derivation and calculation. Ionospheric disturbances were mainly presented as disturbances of ionospheric electric field, magnetic field, total electron content (TEC), critical frequency, etc. The characteristic parameters of the ionosphere can be calculated by the analysis of electromagnetic pulse reflection, and the numerical values of ionospheric disturbances can be extracted. Based on LAIC electric field mechanism hypothesis, the change of atmospheric conductivity above the earth’s surface and the conduction process from ground vertical electric field to the bottom of ionosphere were deduced, starting from air ionization caused by surface radioactivity. According to the critical electric field theory, the atmospheric additional current density and the potential distribution of the ionosphere with the condition of quasi-static electric field were calculated. Finally, the distribution of the horizontal electric field in the ionosphere was obtained by Green’s function method. In this paper, earth’s surface atmospheric conductivity formula based on ground radioactive activity was established, the calculation process of earth’s surface abnormal electric field propagating to ionosphere was improved, and the calculation formula of ionospheric electric field disturbance was given. The calculation process of ionospheric disturbance caused by ground radioactivity anomaly was verified by the observation data of gas radon and earth’s surface electric field instrument. The theoretical calculation results of earth’s surface electric field and ionospheric disturbance are basically consistent with the actual measurement results.