The use of augmented reality technology is becoming a necessity of many cultural heritage sites to stay competitive and attractive to tourists. In this paper, we present an outdoor augmented reality guidance system for ancient rock painting aiming to enhance tourist experience and introduce the culture and historical background. We propose a two-stage approach that combines GPS and featurebased recognition methods. In the first stage, we build a navigation map in advance, which consists of the distribution information of major scenic spots, then visit these spots guided by GPS data on the standard smartphone. In the second stage, we adopt a feature-based recognition and tracking method to identify rock painting accurately and augment them with interactive contextual annotations like 3D textual labels, images, and videos. The reliability of this system is verified through on-site demonstrations - RockArt of the Helan Mountain, which is one of National Key Historical and Cultural Sites in China.