A numerical analysis has been performed for three dimensional developing turbulent flow in a 180° bent tube with roughened wall by algebraic Reynolds stress model which is adopted to solve anisotropic turbulent structure precisely. To our knowlege, very little has been reported about the numerical investigations of bent tube with roughened wall. In numerical analysis, an algebraic Reynolds stress model in conjunction with boundary-fitted coordinate system is applied to 180° bent tube with roughened wall and it with smooth wall. As a result of this analysis, it is found that calculated results show comparatively a good agreement with the experimental data of time averaged velocity and secondary vectors. In bend tube with roughened wall, the location of maximum streamwise velocity moves more remarkably toward the outer wall than it with smooth wall and the intensity of secondary flow increases. These phenomena are realized by the present method. As for the comparison of turbulent energy, the present model has been found to simulate characteristic features of turbulent energy, but it has a tendency to overpredict its value. Moreover, it is elucidated by using calculated results that the decrease of averaged turbulent intensity over cross-section along streamwise is caused by the gradient of stream wise velocity with respect to bend angle.