The sensibility of a waveguide evanescent wave sensor is limited by its evanescent wave intensity. To improve the sensibility of the sensor, the evanescent wave intensity of the waveguide was enhanced by designing a high-refractive-index resin layer on the surface of the waveguide. To optimize the layer thickness, the relationship between the evanescent wave ratios and the layer thicknesses under different refractive index values was studied. A laser-induced waveguide self-written technique was utilized to fabricate an evanescent wave sensor by coating a layer on the waveguide with refractive index of 1.6 and a thickness of 300 nm, respectively. The UV-Vis spectral measurement results show that after the layer coating, the absorption detection limit of Rhodamine B aqueous solution is increased to 1×10^–9 g/mL, which is 10 times enhanced than that of the uncoated sensor. The sensor has the merits of low cost, small size, simple fabrication and high sensitivity, which has broad application prospects in various fields.