Under the early filtered total nitrogen 5 mmol/L, ammonium: nitrate (10∶90) and moderate low light level, hydroponic mini Chinese cabbage seedlings was employed to study NO donor, inhibitor(LNAME，NaN₃) and scavenger(Hb) conducted for 8 days. The morphological parameters and photosynthesis fluorescent parameters of mini Chinese cabbage seedlings were measured. To probe exogenous NO involved in the ammonium and nitrate regulation of mini Chinese cabbage seedlings growth under low light intensity stress. The results indicated that: (1) plants supplied with SNP compared with CK increased chlorophyll content，but had no significant difference in fresh weight of shoot and root，total leaf area, the photosynthetic characteristics and chlorophyll fluorescence parameters. (2) When the NO scavenger (Hb) and inhibitor(LNAME, NaN₃) were added into the ammonium nitrate solution, the shoot and root of fresh weight, total leaf areas, net photosynthetic rate(P_n), stomatal conductance(G_s), maximum quantum yield of PSⅡ(F_v/F_m), electron transport rate(ETR) of plants decreased in different levels. Compared with CK, total leaf area decreased 15%, 24% and 40%, Pn declined 31.2%, 35.8% and 56.7%. Taken all together, NO scavenger and inhibit can obviously eliminate the promotion effect of moderate ammonium: nitrate in mini Chinese cabbages seedling growth under low light intensity. Moreover, exogenous NO has the same function with moderate ammonium: nitrate, which can promote the growth of mini Chinese cabbage seedling under low light intensity stress. Therefore, NO involved in the moderate ammonium: nitrate(10: 90) promotion of photosynthetic characteristics of mini Chinese cabbages seedlings under low light intensity stress.