Taking into account both IASI instrument characteristics and the specific circumstance of GRAPES,a bias correction scheme applicable to operational system is developed for IASI radiances.The scheme utilizes a scan correction and an air-mass correction.Figures show that instead of latitudinal dependency for microwave radiances bias,there is a different scan bias for each of the 2x2 IASI pixels.Scan bias between limb and nadir measurements can be removed with the view angle as independent variable,while the smaller amplitude pixel-to-pixel bias avoided by the way of thinning.Air-mass bias is corrected according to the weather condition at that time,which can be quantitatively represented with predictors computed from the background field.Four predictors are used,including 1000~300 hPa thickness,200~50 hPa thickness,50~20 hPa thickness,and model surface temperature.Verification results show that biases can be controlled stably at a relatively low level for a long time and the correction effects are significant.