The model of MPMD program, which is based on MPI, is quite complex and includes several SPMD programs and their coupler. MPMD model is quite popular in climate domain, and it will be quite practical for the developer to understand its characters. This work focuses on the performance of the coupler module of MPMD program CCSM3.0 to locate the possible load-imbalance problem among the subprograms. The load balance issue of complex MPMD program is simplified down to issues of a set of SPMD programs and their interactions, providing good vision for the developers and performance diagnosing individuals to optimize the program.