Abstract: In order to study the best substrate quantity in the eco-organic soilless culture system, substrate quantity ranged 1~5L per plant on cucumber growth and development were studied. The results showed that cucumber growth and output were affected by the substrates quantity, within the substrates range of 1~5L per plant, the more substrate quantity used, the better of cucumber growth and also the higher output. However, there were no significant differences of growth and output of cucumber between 4L and 5L per plant. Considered the substrates cost, the benefit of 4L per plant were higher than 5L per plant with 370 yuan per 667m2. In order to reduce cost and improve benefits, when rice hull ash and sawdust were used as substrates, 4L per plant, i.e. 8m3 per 667m2, should be used.