To further reduce the lasing threshold of organic semiconductor materials, the surface plasmon resonance effect of silver nanoparticles was investigated. The prepared silver nanoparticle solution was spincoated on glass substrate, and then PS:Alq3:DCJTB organic thin film was spincoated on the surface of Ag nanoparticles, and thus formed a planar waveguide. Pumped by YAG (λ=355nm) laser, the stimulated emission results show that compared with the case without Ag nanoparticles, the Agnanoparticleenhanced edge stimulated emission increases 10.38fold and its lasing threshold reduces to 0.5 mJ/cm2 from 2.0 mJ/cm2. The vertical surface stimulated emission increases 6.13fold and its lasing threshold reduces to about 1.5 mJ/cm2 from 2.5 mJ/cm2. This work may be of great significance in the realization of lowthreshold organic semiconductor lasers.