In order to provide reference for bicycle lane design, conflict between roadside bicycle and automobile was observed on urban road. The influences of the number of roadside bicycle per lane on conflict were analyzed. The models between them were established respectively for arterial road, sub arterial road, and branch road by regression method. One accident per week and month were selected as threshold values and conflict between automobile and bicycle was divided to slight conflict, general conflict, and serious conflict according to the relation between the number of conflict and accident. Based on established models, calculation method of bicycle lane width was given according to conflict grade division, and case study was conducted. It shows that the number of conflict between automobile and bicycle increased with the raise of the number of roadside bicycle and there were quadratic function relations between them for arterial road and branch road and power function relation between them for sub-arterial road. When conflict grade reached serious degree, it was necessary to widen bicycle lane and increase the number of bicycle lane so as to decrease the number of bicycle per lane and conflict between automobile and bicycle and improve safety level of bicycle.