We propose and experimentally demonstrate a chromatic dispersion (CD)-insensitive first-order polarization mode dispersion (PMD) monitoring method based on radio-frequency (RF) power measurement. In high-speed (>10-GSym/s) transmission systems, a narrowband fiber Bragg grating (FBG) notch filter filters out the optical components at 10GHz away from the carrier. After square-law detection, the 10-GHz RF tone changes with PMD and is insensitive to CD, which can be used as a PMD monitoring signal. Compared with the monitoring techniques utilizing clock tone, the PMD measurement range is increased from 26.3-ps to 50-ps while the requirement of the bandwidth of photodetector is reduced from 19GHz to 10GHz in 19-Gsym/s systems. It is experimentally shown that this technique is efficient on CD-insensitive first-order PMD monitoring for 38-Gbit/s DQPSK and 57-Gbit/s D8PSK systems.