Low carbon steel Q235 was firstly conducted by W-Mo-Y double glow plasma surface alloying process.Then the optimal process parameters were confirmed by means of researching the effects of electrode distance, working pressure, holding time, and holding temperature on the thickness of alloying layer. And Optical morphologies, alloying elements distribution and phase composition were analyzed. The results show as follows: the optimal process parameters of W-Mo-Y surface alloying process are as follows: interelectrode distance 25 mm, working pressure 30 Pa, holding time 3 h, holding temperature 1000 ℃. The thickness of alloying layer can reach 37 μm; The microstructure of alloying layer is columnar crystal, and there is anobvious boundary between alloying layer and the matrix. And W and Mo in alloying layer are in gradient distribution. Y is not evenly distributed, and segregate at grain boundaries.