A novel diagnostic system for the real time inspection of small tubes network was developed based on ultrasonic guided wave NDT technology.The diagnostic system consists of a flexible transducer array which employs piezoelectric ceramic as the sensitive element, guided wave excitation/receiving hardware subsystem and data analysis software. The flexible transducer array can be surface mounted in a ring of any size tube’s outer wall,and be able to excite and receive axial symmetric guided waves in tubes.Difference from existing inspection system,the new diagnostic system contains multi channel switch matrix which used for rapid automatic switching the needed signal channels for different tubes inspection.Experimental data shows that the analysis software can identify corrosion damages with more than 3% of the total cross sectional area of the tubes effectively,and be able to real time detection state changes of the tubes,such as corrosion damage extension.The diagnostic system has the advantages of high efficiency and flexibility, and provides an effective means for the real time inspection of small tubes network.