The critical frequency of the ionospheric F layer, f
0F2, is of importance to shortwave propagation and ground-space communications. By using regression analysis of the f
0F2 observational data and solar radio flux F
10.7, a short-term predicting technique of the ionosphere f
0F2 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 f
0F2 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 f
0F2 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.