By means of Monte Carlo simulations together with an ab initio molecular orbital method, we present the influence of trimethylamine N-oxide (TMAO), which is a highly polarized spherical-polyhedron, on the distribution and the alignment of surrounding water molecules. The specific alignment of the average dipole moments of solvent water around TMAO is observed in the MC simulation. The number of water molecules in the first hydration shell from MC simulation was in good agreement with the experimental value. A cluster model of TMAO with 12 water molecules was presented as a representative hydration structure of TMAO.