The turbulent flow and heat transfer in the tunnel laminar flow type clean room is investigated by a numerical simulation. The model clean room is assumed to be a rectngular $5m imes3m$, in which a worktable of 0.75m hight, and 1.5m or 3m long at the floor. Major parameters are the inlet flow velocity, inlet hole size and worktable surface distance. The mean Nusselt number is increased by increasing Reynolds number and can be expressed by the correlation equation.