In order to provide reference for possible capacity calculation and LOS (Level of Service) evaluation of urban arterial road segment, traffic survey was conducted under the interruption of parallel bus stopping. The changing rules of average travel speed and cars' saturated headway with the number of parallel stopping bus were analyzed, and the models between them were established respectively by the regression method. Based on established models, suggested adjustment factors and thresholds of the number of parallel stopping bus were given to calculate possible capacity and evaluate LOS of urban arterial road segment, and a case study was conducted. It shows that average travel speed decreases and cars' saturated headway increases with the raise of the number of parallel stopping bus and there are quadratic function relations between them. The more the number of parallel stopping bus is and the higher road design speed is, the less adjustment factor is, so the influence of parallel bus stopping on road capacity is greater. When the number of parallel stopping bus are the same, adjustment factor of adjacent lane is more than that of interval lane, so the influence of parallel bus stopping on traffic operation of adjacent lane is greater than that of interval lane.