Optical-waveguide surfaceplasmon resonance (SPR) sensorsarecharacterized by smallsizes ,label-freedetection capabilities ,and easeofintegration. In this study ,wedesigned a poly(methyl methacrylate) ( PMMA) ridge waveguide SPR sensor sensitive unit based on a wavelength modulation method and optimized its key parameters. Our analysis results showed thatthe sensor could operate stably within a liquid-refractive-index testing range of1. 33~ 1. 45. In the high-refractive-index detection region ,the sensorexhibited a sensitivity ofup to 10220nm/RIU and ahigh quality factor of173RIU- 1 .