Based on the 11-15 d forecast data of T213 EPS 500 hPa geopotential height and 850 hPa temperature in China and the adjacent regions in January 2008, an interpretation method of extended range forecast product is designed, and the pentad average and pentad anomaly forecast of extended range (11-15 d) are got after the 11-15 d daily forecast data are processed by ensemble mean, moving average of backward decaying weighting coefficient and pentad average. Meanwhile, the forecast effect of the pentad average and pentad anomaly forecast is verified. The results show that ensemble mean and moving average of backward decaying weighting coefficient both can reduce the prediction error and improve the forecast effect. The pentad mean absolute error of the 11-15 d pentad average forecast of 500 hPa geopotential height and 850 hPa temperature are equal to the level of the 5th d forecast of daily control forecast. The pentad anomaly correlation coefficients of 500 hPa geopotential height and 850 hPa temperature are both close to 0.6. Taken as a whole, the forecast effect of 11-15 d pentad average is good enough to use. The phase accuracy rate of 11-15 d pentad anomaly forecast of 500 hPa geopotential height and 850 hPa temperature are both very good in mainland China except for part of the southeast coastal area and the northeast area. In general, the phase accuracy rate of 850 hPa temperature is better than 500 hPa geopotential height. The 11-15 d pentad anomaly forecast can reflect the persistent large scale anomalous anomaly. The range, distribution and center of anomalous anomaly can all be forecasted well but the overall intensity is weaker than observed field.