To　determine　the　effective　moisture　diffusion　properties　of　fiber　polymer-matrix　composites,　a　new　solution　method　was　established　by　using　a　concept　of　unit　cell.　The　effects　of　temperature　and　fiber　volume　fraction　on　the　effective　moisture　coefficients　were　investigated.　In　this　study,　the　impermeable　fibers　were　assumed　to　be　distributed　uniformly　in　matrix.　Using　the　proposed　model,　effective　moisture　diffusivities　were　calculated　at　different　temperatures　and　fiber　volume　fractions.　The　results　show　that　effective　diffusivities　of　the　composites　increase　with　the　increase　of　temperature,　and　decrease　with　the　increase　of　fiber　volume　fraction.　Effective　diffusivities　of　regular　hexagonal　composite　are　a　bit　larger　than　those　of　square　one　under　the　same　temperature　and　volume　fraction.　The　numerical　results　are　compared　with　those　from　empirical　formula,　and　good　agreement　is　achieved.　Therefore,　it　proves　that　the　present　method　is　valid　and　reliable　to　predict　moisture　diffusion　properties　for　fiber　polymer-matrix　composites　by　the　unit　cell　model.　The　present　results　are　significant　to　explore　moisture　diffusion　mechanism　and　overall　properties　of　composites.