Why is the Sydney harbor Brudge an icon and a tourist attraction in Sydney?

Basically because it was one of the largest bridges of its time, with over 10 lanes for traffic, and lanes for trains too. It's quite a simple structural shape, similar to a coat hanger, hence its nickname.

Sydney harbour bridge is the world's widest long-span bridge . It took 9 years for its construction completion .It was opened in 1932. Bridge length is 1,150 m. It has a bow shape too. Because of this features , it is a tourist attraction in Sydney . In Sydney first attraction comes in every person's mind is Sydney harbour bridge and opera house.

Other attractions include :
http://www.sydneythingstodo.com.au/