Abstract: Objective We introduce a measurement for extracting the regional ionosphere TEC(total electron con-tent)from GPS dual observations in detail.From the basic principles for extracting TEC using GPS,we focus on solving two key problems.One was to improve the accuracy of pseudo-range observa-tions,and the other was to detach the DCB(differential code bias)of the satellites and receivers.Fur-thermore,the extracted TEC and TEC calculated by the CODE(Center for Orbit Determination in Eu-rope)were used as an ionospheric delay correction in a single-frequency point positioning model.Theresults show that the point accuracy can reach to 0.2-0.4musing the extracted TEC correction,a sig-nificantly improvement over the use of an interpolated GIM correction.