In China, nitrogen fertilizer application rates in intensive agricultural systems have increased dramatically in recent years, especially in protected vegetable production systems. This excessive use of nitrogen fertilizer has resulted in soil secondary salinization (SSS), which has become a significant environmental stress for crops such as cucumber, in the protected farmland of China. So it is necessary to propose some guidelines to direct the management of SSS in facility agricultural areas. In this study, the NO₃^-1-SSS classification was studied in greenhouses planted with cucumber ( Cucumis sativus L. cv. Dongfangmingzhu) in Taizhou, Jiangsu Province, East China. After the soils in these greenhouses were treated by different concentrations of nitrate, the SSS levels expressed by electrical conductivity (EC) were studied at 0.89 dS m^-1 for control, 2.78 dS m^-1 for treatment 1 (T1), 3.65 dS m^-1 for treatment 2 (T2), 4.66 dS m^-1 for treatment 3 (T3) and 6.15 dS m^-1 for treatment 4 (T4). The results showed that there were significant relationships between NO₃^-1 contents and soil EC in the surface soils, implying that the change in soil quality resulted from the difference of nitrate contents could be expressed by the level of the NO₃^-1-SSS. The level of the NO₃^-1-SSS was significantly related with the cucumber height and yield (p < 0.05). Then, the classification for NO₃^-1-SSS in cucumber-based greenhouse in Yangtze River Delta was identified as five levels according to the effects of SSS on the cucumber height and yield (level Ⅰ: EC < 2.03 dS m^-1, level Ⅱ: 2.03 dS m^-1 < EC < 3.76 dS m^-1, level Ⅲ: 3.76 dS m^-1 < EC < 5.32 dS m^-1, level Ⅳ: 5.32 dS m^-1 < EC < 6.15 dS m^-1, level Ⅴ: EC > 6.15 dS m^-1).