Abstract: On the basis of the ionosonde data,this paper deals with the diurnal morphology of the plasma vertical drifts near the ionospheric F₂ peak by means of Servo Model.And corresponding variations of the drifts with season and solar activity are also discussed over a group of lower mid-latitude locations.The results indicate a roughly good consistence with the experimental ones,while some new features,mainly the "hollow-at-dawn" and "buldge-at-sun-rise" on the diurnal curves,are discovered.