Abstract: The critical frequency of the ionospheric F layer, f₀F₂, is of importance to shortwave propagation and ground-space communications. By using regression analysis of the f₀F₂ observational data and solar radio flux F_10.7, a short-term predicting technique of the ionosphere f₀F₂ is introduced. The solar activity index fc, defined as the moving average of F_10.7, is used as the input, and the output is the ionospheric critical frequency f₀F₂ values three days in advance. Historical data from eight ionospheric stations around China is used to build the method and verify the performance respectively. The results are compared by giving their root-mean-square errors according to different solar activity, season and local time. The results show that the predicting errors at each season and local time are acceptable, which indicate that the method can forecast the f₀F₂ values effectively. The predicting errors at low latitude are higher than those at middle latitude, which conform the complexity variations of low latitude ionosphere. In addition, this method can also be applied to the short-term forecasting of other ionospheric parameters.