Abstract: The Penglai and Shaximiao formation in Xinchang gas field of Sichuan belongs to lower penetrate and higher irreducible water rate reservoir. It is ensured that the formation was severely damaged, so analysis and test research of the damaging factors was necessary. The research effect shows that the main damaging factors are water sensitivity and water locking, which caused by out-injection liquids. The secondly was alkalis sensitivity damage. Corresponding propose were put forward aim at the damaging factors.