Comparative experiment of 3 medium sand columns was executed to research the influence of water content on natural attenuation of diesel fuels contaminated vadose zone. The results showed that: The lower the water content, the stronger capacity of retarding diesel fuels was. After a diesel fuels spill, the average concentration of TPH were 57.7 g•kg-1, 47.55 g•kg-1 and 31.95 g•kg-1 in medium sand with different water content (0.66 %, 8.00 % and 15.22 %). Besides, the TPH found 90 days after the natural attenuation degradated by 38 % and 44.62 % 4 of the initial contaminant load of the medium sand with water content 0.66 % and 8.00 %. Additionally, the higher the water content, the larger the microbial activity of sand was. Biodegradation was the important mechanism for natural attenuation of diesel fuels.