A process used by the software industry to design, develop and test high quality software is called software development life cycle. The main aim of SDLC is to produce high quality software that meats customer expectation. We can also refer SDLC as Application Development Life Cycle. SDLC is not a methodology it is a description of various phases that are involved in software development starting from project definition to deployment and sustainment. These SDLC phases serve as a programmatic guide to project activity. In our paper we have explain various SDLC models (Waterfall, Spiral, V-Model, Iterative, Big Bang, Agile and Rapid Application Model).