Automatic data distribution is a key technique in the area of automatic program parallelization for MPP(massively parallel processing) systems. Data distribution schemes directly influence the parallel execution performance of application programs in MPP systems. Taking MPP Fortran as an example, this paper discusses techniques of automatic data distribution in detail such as alignment analysis, shared array distribution, performance estimation for shared array distribution schemes, and shared array redistribution. The corresponding algorithms are presented and they will be implemented in these automatic program parallelization tools for MPP Fortran.