The invention provides an ultra wide band ladder-shaped FM/CW laser radar ranging system based on the double-parallel MZM, and belongs to the field of laser range finding. Problems of limited modulation band width of a traditional FM/CW laser radar, and difficulty in improving of range finding precision are solved. A fiber loop formed by a single-frequency continuous laser, a double-parallel MZM and a fiber laser amplifier, and a tunable F-P fiber filter form a signal modulation system to generate ladder-shaped frequency modulation signal light. The signal modulation band width can reach dozens of GHz to hundreds of GHz. A receiving end carries out resolving on a target echo wave by adopting the centroiding algorithm, and principle errors caused by the ladder-shaped frequency modulation signals are inhibited by use of the double-balancing inhibition principle, so range finding precision of the system is further improved. The radar ranging system is mainly used for range finding for the to-be-measured objected.