Penetration of chloride ions into concrete and diffusion of moisture in concrete are important factors responsible for the corrosion of steel in concrete. The two diffusion processes are coupled. This paper deals with the analysis and simulation of coupled chloride penetration and moisture diffusion in concrete. Of particular interest is the parallel programming in finite element method for solving the coupled diffusion problem. Parallel computing technology has been advantageous for solving computationally intensive problems. It has become quite mature technology and more affordable for general application. Our approach to solve the parallel programming problem is to use available libraries, i.e. Portable, Extensible Toolkit for Scientific Computation (PETSc) and The Message Passing Interface (MPI) standard. The formulation of the coupled diffusion problem, the material models involved in the differential equations, the details of parallel domain decomposition technique in the finite element algorithm are presented. The advantages of parallel programming are demonstrated by a numerical example.