In this paper, a mm-wave radar is devised to monitor the micro-deformation of bridges and its performance is verified via monitoring a highway and a freight railway bridges. The radar interferometry technology is utilized to develop the compact and portable mm-wave radar. Experiments are set up to monitor a highway bridge around Beijing-Tianjin expressway which is near the sixth ring roads of Beijing and a Daqin freight railway bridge in Yanqing, Beijing. The experimental results demonstrate that the devised radar can detect the micro-deformation of the bridge vibration with a super-resolution and high precision, making the mm-wave radar promising for bridge monitoring, dam monitoring, debris flow monitoring applications.