Abstract: Before the acid treatment of the damaged wells, identification and diagnosis of the damage on gas/oil well is of great significance in such aspects as the determination of the treatment scale, optimizing the treatment parameters, bettering the plan of treatment design and so on. By analysis and study of various damage-inducing factors, a program of identifying and diagnosing damage is introduced in this paper which incorporates predicting and diagnosing models of 6 types of damage, and the field application of which yields satisfying results.