The bend is often encountered in routing the differential microstrip lines on PCB layers for high-speed transmission. In addition to generating unwanted electromagnetic wave in air, a bend of differential transmission line also causes random ultra phase difference other than 180 degree for the original odd mode. In this paper, the effect caused by the bend of differential microstip line is demonstrated and analyzed. Importantly, a technique for redressing the ultra phase difference is proposed. Both of simulation and measurement results are presented in this work.