Aiming at the technical bottlenecks commonly faced by reverse osmosis (RO) systems for coal chemical wastewater reuse, such as severe concentration polarization, frequent membrane fouling, and insufficient desalination efficiency, this study took a large coal-to-olefins project as the research object. By comparatively analyzing the long-term operating data of an on-site first-stage two-section RO system without an interstage booster pump and a pilot-scale RO system with an interstage booster pump, the impact mechanism of the interstage booster pump on the core performance of the RO device was systematically explored. The results showed that the interstage booster pump could increase the overall desalination rate of the system by 2%~3% by improving the feed water pressure and membrane surface flow rate of the second section, reduce the conductivity of the second-stage product water from more than 175 μS/cm to about 51 μS/cm, and extend the chemical cleaning cycle from 10~15 days to more than 45 days, which significantly reduced the membrane fouling rate and prolongs the service life of membrane elements. The optimal feed pressure for the second stage was determined to be 1.2 MPa, which represented the optimal balance point among energy consumption, membrane service life and cleaning cost. Through pilot-scale verification and mechanism analysis, this study provides quantitative data support and engineering practice guidelines for the design optimization of RO systems for high-salt wastewater reuse and the transformation and upgrading of existing systems.