Abstract: The ionospheric F₂ critical frequency f_oF₂ is one of the most important application parameters in the fields of short-wave communication, detection and electronic countermeasures. Based on the ionosonde data from the Global Ionospheric Radio Observatory (GIRO), the ionospheric CCIR/URSI coefficients are adjusted by the stepwise linear optimal estimation method to reconstruct the ionospheric f_oF₂ in the middle and low latitudes of the world. The results of ionospheric f_oF₂ reconstruction from 2010 to 2016 show that the reconstruction error in mid-latitude region is lower than that in low-latitude region in latitude variation. In the annual change, the absolute error and root mean square error of reconstruction have a tendency to increase with the increase of solar activity intensity, and the relative error of reconstruction has no obvious annual change. In the seasonal variation, the reconstruction error in summer is the smallest, with little difference in the other three seasons. Compared with the IRI model, the absolute and root mean square errors of ionospheric f_oF₂ reconstruction are reduced by 38% and 34% respectively, which proves the validity and reliability of the proposed method.