At last I find the answer of my question. This class convert the byte[] to valid security decriptor comobject.
ActiveDs.ADsSecurityUtility secUtility = new ActiveDs.ADsSecurityUtility();
ActiveDs.IADsSecurityDescriptor sd = (IADsSecurityDescriptor)secUtility.ConvertSecurityDescriptor((byte[])attribute[0], (int)ADS_SD_FORMAT_ENUM.ADS_SD_FORMAT_RAW, (int)ADS_SD_FORMAT_ENUM.ADS_SD_FORMAT_IID);