To explore ways to control nitrogen leaching loss from protected vegetable production systems during the summer fallow season and hence to mitigate the risk of N pollution of groundwater in the Taihu Lake region, a field experiment was conducted to evaluate effects of planting sweet corn as catch crop on NO3^--N content, soil electrical conductivity and pH in soils different in N application rate and further to observe its effects on nitrogon leaching using lysimeters and on yield of the following crop, lettuce. It was found that relative to fallow, planting sweet corn as catch crop reduced soil NO3^--N concentration from 251.4 mg kg^-1 to 143.5 mg kg^-1 in the surface soil layer (0~10 cm) and by 4.2%~30.7% in the top soil (0~50 cm). Besides, it reduced soil conductivity significantly, or by over 30% in the surface soil layer, but did not affect pH much. Although planting sweet corn didn’t affect volume of leachate, it did reduce the total N concetration from 102.6 mg kg^-1 to 53.7 mg kg^-1 in leachate from plots receiving a high rate of N fertilizer under the conventional management practice. Compared with the fallow treatment, the sweet corn treatment reduced the total N leaching by 30.4% , which, however, did not have any effect, either positive or negative, on yield of the succeeding crop, lettuce. The findings indicate that in summer, the protected vegetable land in South China can be used to plant sweet corn as catch crop, instead of being left in fallow, which can be extrapolated as an efficient approach to reducing the risk of nitrogen leaching.