Abstract: In order to provide irrigation references for industry culture of cucumber plug seedings, with cucumber (Cucumis sativus L.) variety Jinyou 1 as test material, the effects of different irrigation threshold treatments on dry matter accumulation, root activity, photosynthesis, chlorophyll fluorescence parameters were studied by using vinegar residue as plug seedling substrate. The experiments were conducted with four treatments with the irrigation threshold at 65%, 55%, 45%, 35% of the relative water content of medium respectively. The results showed that when the irrigation threshold was 55% of the relative water content of medium, the accumulated dry matter, length of taproot, root activity of seedlings and photosynthetic capacity were greater than those of seedlings under other irrigation threshold, followed was the 45% treatment. So it was suggested that 45%-55% of the relative water content of medium can be the optimum irrigation threshold in cucumber plug-seedlings raising.