The forecasting problem whose sample data including real number and interval grey number is studied. An interval grey number sequence is converted into a real number sequence by calculating the areas of grey number layers and the cognition of interval grey number. The areas of grey number layers and the cognition of interval grey numbers are predicted respectively. Then the unbiased prediction model of the interval grey number is achieved by deducing and reverting. Comparisons real example from the reference with the unbiased prediction model demonstrates that the unbiased prediction model is more accurate than other models, it is shown that this method is effective and applicable, and can avoid the calculation of interval grey number.