Wireless sensor networks are currently growing area for Research and Development because sensor network constitute platform for many applications related to environment monitoring ,health care, surveillance, military. Coverage area is most challenging task in wireless sensor network. Coverage in a wireless sensor network can be thought of as how well the wireless sensor network is able to monitor a particular field of interest. Ensuring sufficient coverage in a sensor network is essential to obtaining valid data. The coverage problem can be approached in many different ways. The needs of a particular deployment will heavily influence the coverage scheme choosen.Several coverage strategies are used in wireless sensor network in order to deploy sensors in such a way so that region of interest can be covered completely.Strategies are categorized into three groups; Force Based, Grid Based and Computational Geometry Based Approach.