An ordinary prism coupling surface waves (SW) sensor and grating-assisted SW sensors are studied using rigorous coupled-wave-analysis method. The material parameters and structural parameters of the one-dimensional photonic crystal and grating are designed, which works under 1550 nm. The depth of grating is 20 nm, the pitch is 524.6 nm, and the duty cycle is 0.5. Simulation shows that grating leads to the emergence of dual-resonance dip, and the surface mode is splitted. The use of double resonance dip characteristics can improve sensitivity of the perspective of an ordinary prism structure SW sensor more than 3 times.