Multipath interference is a typical scenario in GSM-R network optimization. It generally occurs in areas with overlapping coverage from multiple optical fiber remote units. The rapid digital and intelligent transformation of railway mobile communication system has exposed limitations in conventional GSM-R multipath interference optimization approaches. Conventional methods can no longer meet the needs of modern rail transit for high efficiency, accuracy, and intelligent decision-making capabilities. The principles and scenario characteristics of GSM-R multipath interference are introduced in this paper. In addition, the core modules and system architecture of the ray tracing driven high-speed rail wireless network optimization system are analyzed. Taking the voice quality optimization in Wuhan-Guangzhou high-speed railway mountains and tunnels scenario as a case study, the high-speed railway wireless network optimization system successfully identified the causes of voice quality degradation. Furthermore, three network optimization schemes are proposed and simulated. The simulation results show that by adjusting the transmission power and antenna down-tilt angle of optical fiber remote unit, the multipath interference problem at the start point of voice quality degradation is significantly solved. This paper provides a solution reference and technical accumulation for the digital and high-quality optimization of GSM-R network multipath interference.