Langmu Si Town locates at the border of Sichuan-Gansu. This village hosts two Gelugpa Tibetan Buddhist monasteries - Kirti Monastery in Sichuan Province and Sertri Monastery in Gansu Province, which are not far from each other.

The Monlam Prayer Festival comes from the prayer festival held in 1409 by the Buddhist master Tsongkhapa at the Jokhang Monastery in Lhasa, which spread well in monasteries of South Gansu, and have become a significant festival for South Gansu Tibetans. It lasted 15 days from the evening of the 3rd January to the 17th January of Tibet Calendar. The main purpose of the Prayer Festival is to pray for longevity of the highest spiritual masters and Lamas and for Dharma (Buddhism) been last forever as long as the sky still blue, and for welfare of all the living creatures, and for peace and love of all world.

On the 13th January, the Thangka Festival takes place in Langmu Si and starts at 9 o'clock in the morning. Under the mysterious and solemn Buddhist music played by such instruments as Suona, drums and gongs, the monastery's master lets the monks carry a huge thangka with Buddha image from the prayer hall. The Thangka, surrounded by numerous faithful, is brought to the nearby mountain and placed on the hillside.

The ceremony is host by Khenpo, the sage of the monastery. All the monks read the sutras with great piety to thank the mercy of the Buddha. Subsequently, the monks and the faithful successively devote Hada to the Buddha. Then the giant thangka is slowly unfolded out. The devout believers bow down and kowtowing, mumbling the Buddhist sutras in front of the Buddha image and praying for well-being and happiness for the family. The ceremony lasts about 1 hour. Afterwards, the placed Thangka is carefully rolled up again and carried around the monastery by the monks to circumnavigate it. In the end, it will carry back to the monastery. All Thangkas for the ceremony belong to the treasures of the monastery. Langmu Si Monastery houses many different thangkas with motifs of Tsongkhapa, Sakyamuni, Maitreya, etc., which are alternated year after year and put on display.