Abstract: In order to promote the application of vinegar residue substrate as seedlings substrates, according to large granule and high porosity of vinegar residue substrate, the experiment was carried out with semi-wet sieve to study the effect of different grinding extent of residue substrate on growth and photosynthesis of pepper seedlings. The results showed that with the increase of grinding extent, dry bulk density, saturated bulk density, water-holding porosity (WHP) and WHP/AP of vinegar residue substrate were gradually increased, while total porosity, aeration porosity (AP) were gradually reduced. With vinegar residue substrate semi-wet grinding (diameter of sieve was 6 mm) only once (T2), the growth of pepper seedlings was improved, the photosynthetic pigment contents, net photosynthetic rate (Pn) and actual photochemical efficiency of PSⅡ(ΦPSⅡ) were obviously increased. The above results showed that vinegar residue substrate semi-wet grinding (diameter of sieve was 6 mm) only once (T2) was the optimum grinding extent for growth of pepper seedlings.