Overhead catenary is an important device for traction equipments of electrical railway, therefore the condition of overhead catenary will impact the operation safety for the railway. In order to design a set of device on the operating EMUs to monitor the operation state of the catenary in the whole process, starting from the design requirements, design principles and design scheme of the system, the non-contact image processing, machine vision and infrared temperature measurement key technologies were introduced to complete the system design of the device, and the performance of the device was verified through static and dynamic tests. According to the feedback of test and field application, the device met the requirements of technical conditions. Meanwhile, the detection results of the device on the catenary could provide basis for the maintenance of the catenary.