Surface roughness on blaze plane of silicon echelon grating can induce the scattering of incident light, which means that the size of surface roughness is important to the application of echelon grating in spectrometer industry. In order to reduce the scattering light of echelon grating, an important thing is to decrease the surface roughness on blaze plane of echelon grating. In the silicon wet etching process, the pseudo-mask is formed by the hydrogen bubbles generated during the etching process, which causes high surface roughness and poor surface quality. Based upon the ultrasonic cavitation and wettability enhanced by isopropanol (IPA), ultrasonic vibration and wettability enhancement are used to improve surface quality of echelon grating during silicon wet etching process. The surface roughness is smaller than 15 nm when using ultrasonic vibration and it is smaller than 7 nm when using wettability enhancement. Combining ultrasonic vibration and wettability enhancement,the surface roughness is smaller than 2 nm when the range of IPA mass fraction, ultrasound frequency and power is 5%~20%, 100 kHz and 30~50 W, respectively. The surface roughness is equal to 1 nm when the range of mass fraction of IPA and ultrasound power is 20% and 50 W and the ultrasound frequency is 100 kHz. The experimental results indicate that the combination of ultrasonic vibration, wettability and optimizing of experimental parameters can fabricate the echelon grating with lower surface roughness.