Xiongyan21
You have not defined the MPI env. variables yet.
Please use the following
export MPI_INCLUDE=/usr/local/Cellar/mpich2/3.1.2/include
export MPI_LIB=/usr/local/Cellar/mpich2/3.1.2/lib
export LIBMPI=" -lmpifort -lmpi -lpmpi -lpthread"
PS Use of CAPITAL LETTERS in a forum entry is not considered very polite