Social robot behavior should conform to human social conventions. Social conventions concerning the social distance for interaction, the silence distance for non-disturbing, the safety distance for avoiding collision, the left-side passing-by preference, and the face-to-face communication rule are embedded in the motion planning procedure. Potential-field-based motion planning algorithms are designed in this paper, which not only considers the above-mentioned social conventions but also takes stationary obstacles and pedestrian avoidance into account. Simulations in different cases are conducted to verify both the effectiveness of the potential field and the compliance with the social conventions.