In　order　to　improve　and　perfect　the　design　calculation　content　for　crack　width　of　continuous　steel-concrete　composite　beams　in　the　negative　bending　area,　a　crack　width　calculation　formula　is　deduced　based　on　the　stress-strain　constitutive　laws　of　steel　concrete,　and　experiments　are　conducted　on　composite　steel-concrete　beams.　The　formula　has　taken　into　considerations　the　behavior　of　composite　beams　before　and　after　concrete　cracking　and　influence　of　relative　slippage　between　the　steel　beam　and　the　concrete　on　crack　width.　The　calculated　results　are　in　good　agreement　with　experiment　and　except　that　there　is　certain　structural　crack　width　which　is　in　the　permissible　range.