The flow of electric currents in the dynamo region (90-150km) of the ionosphere generates regular daily variations of the magnetic field observed at ground bases and middle latitudes, called Sq (solar quiet) by Chapman and Bartels (1940) or SR (Solar regular) by Mayaud (1967). This thesis, we study the regular variation of the magnetic field in Vietnam in the overall framework of relations Sun-Earth's and ionosphere modeling. The first chapter presents an all concepts necessary for the sun, the solar magnetic field the Earth's magnetic field, and the interaction between the sun and the earth of the thesis. The second chapter presents solar and magnetic indices, parameters of the solar wind, magnetic observations, ionospheric data, and models MSIS90 and TIEGCM useful. In chapter 3, we present the results obtained from magnetic observations on the regular variation and characteristics of Sq during Solar Cycle 23 at Phu Thuy- Vietnam. The results concerning the analysis of ionospheric parameters over several solar cycles at Phu Thuy, Vietnam and model of ionospheric conductivity in Vietnam. The final chapter uses the simulation of long-term variations of the critical frequency foF2 of the F2 region by TIEGCM NCAR to study the long-term variation of foF2 observed at Phu Thuy. This model allowed us to study the tidal influences diurnal and semi diurnal migrants, migrant non-diurnal and semi diurnal lower atmosphere, and changes of geomagnetic activity on the long-term variation of foF2
