Abstract: Analog Deviation is introduced to evaluate the analog degree between two samples, and tests of Analog Prediction Method for 24 h ahead forecast of ionospheric TEC detected by Xiamen station in 2004 have been conducted in this paper. The results reveal that the relative error has good relationship with the geomagnetic activities, and it will be larger under geomagnetically disturbed conditions than undisturbed ones obviously, reaching 100% indeed; as a whole, the relative error is 18.022%, 44.896% and 11.676% under conditions of geomagnetic disturbances and undisturbed respectively. The cumulative proportions of relative error under 10%, 20%, 30%, 40% are 38.209%, 65.075%, 84.984% and 90.448% respectively. The Analog Prediction Method is based on the autocorrelation method, with the observed ionospheric TEC to predict, but only choosing the 24, 48, 72 h data which will have best analog with the predictions. The result of forecast will be much more better on condition of using ionospheric TEC in mid-latitude or under geomagnetic undisturbed conditions.