For the purpose of the improving the efficiency of the 4H-SiC photodiode, we reported the spectral reflectance of the antireflection structure of the 140nm period like Moth Eye structure on the 4H-SiC pn epi-wafer. Measured reflectivity of the antireflection structured surface is below 2% at 310nm. The peak responsivity of SWS photodiode is 170mA/W (QE=75%) at 280nm. The response cut-off wavelength is 380nm. Sensitivity of the sensor with SWS structure has increased by compared with that without SWS structure over 260nm of wavelength. At 310 nm, the sensitivity of the photodiode with SWS has increased by 1.3 times than that without SWS. Total amount of short circuit currents was 22% of increase.