  In this work, a gradual solar energetic particle (SEP) event observed by
multispacecraft has been simulated. The time profiles of SEP fluxes accelerated
by an interplanetary shock in the three-dimensional interplanetary space are
obtained by solving numerically the Fokker-Planck focused transport equation.
The interplanetary shock is modeled as a moving source of energetic particles.
By fitting the 1979/03/01 SEP fluxes observed by Helios 1, Helios 2, and IMP 8
with our simulations, we obtain the best parameters for the shock acceleration
efficiency model. And we also find that the particle perpendicular diffusion
coefficient with the level of $ \sim 1\% - 3\% $ of parallel diffusion
coefficient at 1 AU should be included. The reservoir phenomenon is reproduced
in the simulations, and the longitudinal gradient of SEP fluxes in the decay
phase, which is observed by three spacecraft at different locations, is more
sensitive to the shock acceleration efficiency parameters than that is to the
perpendicular diffusion coefficient.
