Do you mean you have an ENVI series file as discussed here?
http://www.harrisgeospati...emporalAnalysis.html

This file points to the individual rasters in the series, which are already separate files and/or bands.
Or do you mean you want to save out individual bands from a multi-band file?

Thanks alot for your care,

I mean I have an ENVI series file which contain more than 400 tifs, I want to convert it to individual tifs.

An ENVI '.series' file does not contain actual data. It references files on a system like a metadata file. For example, here is one file referenced in an ENVI .series file:
------------------------------------------------
"FORMAT": "ENVI",
"FORMAT": "ENVI",
"URI": "C:\\Data\\LasVegasTimeSeries\\Gridded\\OSAVISeries\\OSAVILasVegasMay1975.dat",
"TIME": "1975-05-13T17:34:00.0Z",
"PIXEL_SIZE": [
30.000000000000000,
30.000000000000000
],
"SPATIAL_REFERENCE_TYPE": "STANDARD",
"BANDS": 1,
"BAND_NAMES": [
"Optimized Soil Adjusted Vegetation Index"
],
"DATASET_INDEX": 0,
"COLUMNS": 1832,
"ROWS": 1666,
"UPPER_LEFT_MAP": [643477.88100000005, 4029504.9449999998],
"UPPER_LEFT_PIXEL": [0.00000000000000000, 0.00000000000000000],
"COORDINATE_SYSTEM_STRING": "PROJCS[\"WGS_1984_UTM_Zone_11N\",GEOGCS[\"GCS_WGS_1984\",DATUM[\"D_WGS_1984\",SPHEROID[\"WGS_1984\",6378137.0,298.257223563]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Transverse_Mercator\"],PARAMETER[\"False_Easting\",500000.0],PARAMETER[\"False_Northing\",0.0],PARAMETER[\"Central_Meridian\",-117.0],PARAMETER[\"Scale_Factor\",0.9996],PARAMETER[\"Latitude_Of_Origin\",0.0],UNIT[\"Meter\",1.0]]"
},
"TIME": "1975-05-13T17:34:00.0Z",
"PIXEL_SIZE": [
30.000000000000000,
30.000000000000000
],
"SPATIAL_REFERENCE_TYPE": "STANDARD",
"BANDS": 1,
"BAND_NAMES": [
"Optimized Soil Adjusted Vegetation Index"
],
"DATASET_INDEX": 0,
"COLUMNS": 1832,
"ROWS": 1666,
"UPPER_LEFT_MAP": [643477.88100000005, 4029504.9449999998],
"UPPER_LEFT_PIXEL": [0.00000000000000000, 0.00000000000000000],
"COORDINATE_SYSTEM_STRING": "PROJCS[\"WGS_1984_UTM_Zone_11N\",GEOGCS[\"GCS_WGS_1984\",DATUM[\"D_WGS_1984\",SPHEROID[\"WGS_1984\",6378137.0,298.257223563]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Transverse_Mercator\"],PARAMETER[\"False_Easting\",500000.0],PARAMETER[\"False_Northing\",0.0],PARAMETER[\"Central_Meridian\",-117.0],PARAMETER[\"Scale_Factor\",0.9996],PARAMETER[\"Latitude_Of_Origin\",0.0],UNIT[\"Meter\",1.0]]"
},
-------------------------------
Note that it references a file on disk here: "URI": "C:\\Data\\LasVegasTimeSeries\\Gridded\\OSAVISeries\\OSAVILasVegasMay1975.dat",

So I don't understand what you mean by series in this case. The files are already on disk.
If you have bands in a single file and you want to save out each band, then you would open the data in ENVI and use File->Save As and you can choose TIFF as the output.

Really thanks for you help.