I don't see you setting the pixel size within the call to CONVERT_MODIS_DATA. It looks like the keywords to use are: OUT_PS_X, OUT_PS_Y according to the help document that comes with the toolkit: CONVERT_MODIS_DATA [,IN_FILE=string] [,OUT_PATH=string] [,OUT_ROOT=string] [,/L1A] [,/L1B] [,/MOD14] [,/HIGHER_PRODUCT] [,/SWATH] [,/GRID] [,SWT_NAME=string] [,GD_NAME=string] [,SD_NAMES=string array] [,OUT_METHOD={0 | 1 | 2}] [,GEOLOC_FILE=string] [,OUT_PROJ=envi projection structure] [,OUT_PS_X=double] [,OUT_PS_Y=double] [,NUM_X_PTS=integer] [,NUM_Y_PTS=integer] [,INTERP_METHOD={6 | 7 | 8}] [,/BOWTIE] [,CALIB_METHOD={0 | 1 | 2}] [,SD_POS=integer array] [,/NO_MSG] [,BACKGROUND=integer or float], FILL_REPLACE_VALUE=integer or float] [,R_FID_ARRAY=variable] [,R_FNAME_ARRAY=variable] Additionally, it states you must set the GRID keyword: OUT_PS_X (optional) Set this keyword to a double-precision value containing the X pixel size of the output image. You should specify the pixel size in the units contained in the projection structure passed to the OUT_PROJ keyword. This keyword is ignored unless the /GRID keyword is set. OUT_PS_Y (optional) Set this keyword to a double-precision value containing the Y pixel size of the output image. You should specify the pixel size in the units contained in the projection structure passed to the OUT_PROJ keyword. This keyword is ignored unless the /GRID keyword is set.

Thanks for your reply. But MOD04 dataset is not the grided product (it is swath product), so this keyword doesn't work in my pro. As noted that "This keyword is ignored unless the /GRID keyword is set." Is there any other idea? Thanks.

It sounds like the tool only allows you to specify the output pixel size for gridded datasets. In this case, use the pixel size default and resample to your desired pixel size after the dataset is extracted.