Hi Lizhi,I have mm5 model output files with a lambert conic projection and have used visad to view them. I can hopefully help out. Basically, you need to inspect the BigHeader sections, from which you can derive the parameters that Tom mentioned. I have Java code for inspecting an mm5 file, including BigHeader, SubHeaders and data fields.
FWIW, I prefer the ucar.unidata.geoloc.projection classes in the IDV/Netcdf jars to the native visad.georef ones. Stuart