With the arrival of aging society, the passive robot walking helper is introduced to provide safe mobility for the elders, which features continuous energy dissipation from the system and is thus intrinsically safe. As both static and moving obstacles may be present in daily activities, obstacle avoidance during guidance is very imperative for its practical use, which motivates us to propose such a scheme based on receding horizon control. With a desired goal to reach, the proposed scheme first plans a smooth path for the walking helper to follow. A novel strategy, combined with receding horizon control, is then proposed to avoid the incoming obstacles detected by the equipped sensing system. Experiments based on our developed passive robot walking helper, i-Go, are conducted in real environments to demonstrate the effectiveness of the proposed scheme.