Abstract: Several forms of the driven potential φ₀(t) on ionospheric polar boundary were used to calculate the time evolution of the region 2 field-aligned current J_∥² and the ionospheric electric field E (t).Calculation indicates that when φ₀ increases first,and decreases then,similar tendency is shown in variation of ](2) and E in high-latitudinal ionosphere,though reach their maximum a bit later;so when the driven potential begins reducing,the J_∥² and E,however,continue their enhancing.The time delay of J_∥² and that of E are both related to the relaxation time of the variation of J_∥² when φ₀(t) is a step function,but the delay of ?is a bit shorter.They also depend on the form of the φ₀(t).The retardation time can be longer than 1 hour when φ₀(t) decreases slowly after a sudden increasing.This result is coordinated by the data observed during strong magnetic storms.The response of E-field in the middle latitude ionosphere is somehow different.It increases when φ₀(t) increases,and decreases asφ₀(t) decreases.The evolution of the J_∥² and E is also controlled by the ionospheric conductivity.