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In this paper, we propose and demonstrate a millimeter-resolution long-range optical frequency domain reflectometry (OFDR) using an ultra-linearly 100-GHz swept optical source realized by injection-locking technique and cascaded four-wave-mixing (FWM) process. The ultra-linear sweep is realized using an external modulation method with a linearly swept radio frequency (RF) signal. The RF signal sweeps from 16 GHz to 19.3 GHz, and the slave laser is injection-locked to the 8th-order sideband of the master laser, achieving a frequency sweeping span of ~25 GHz. By using the injection-locked frequency-swept laser as the optical source of OFDR, we obtain a spatial resolution of 4.2 mm over 10-km measurement range. A polarization beat length of 10.5 cm is measured benefiting from the high spatial resolution. To improve the spatial resolution further, FWM process is used to broaden the frequency sweeping …