Abstract: 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.