Modernizing scientific legacy system to object-oriented platforms has been a challenge for the research community over the past few years. It is infeasible to rewrite the entire software with new design rules. The practice of software development continues to shift towards the reuse of legacy systems to handle the complexities of software development. Object-oriented programming enables us to reuse the code by organizing the system into objects by information hiding, encapsulation, polymorphism and other techniques, which results in increased flexibility compared to non objectoriented systems. In this paper, we propose a new four phase process for modernization of legacy systems reusing the existing code. The paper proposes how the computing community can change programming paradigm to take an advantage of modern software design principles, particularly object-oriented programming. This process can be used to convert legacy FORTRAN code into a new object-oriented implementation written in a language such as C++.