This paper introduces an on-line test system of high and low temperature based the Optical Time Domain Reflectometer（OTDR）

which is used to test the additional attenuation of optical cables. Using the computer to communicate with OTDR

high and low temperature boxes and other devices

the attenuation information of the optical fiber in the optical cable is obtained one by one channel. Microsoft Visual Studio IDE is used to software development for processing and display data. And the additional attenuation characteristic parameters of the tested optical fiber are also obtained. The system is easy to operate

and the software interface is highly interactive and can be used for simultaneous detection of multiple optical cables.