Nitrogen (N) fertilizer is known to improve the quality and biomass of vegetables, but it is unclear how to manage the large amount of NO3-N that accumulates in the soil after vegetable harvest. In this study, we examined the influence of irrigation level and irrigation frequency on the growth and soil residual NO3-N of the catch crop mini Chinese cabbage (Brassica pekinensis) in a greenhouse. Using conventional border irrigation with adequate water supply as a control (CK), three irrigation levels (WH: 160% crop evapotranspiration (ETc), WM: 120% ETc and WL: 80% ETc) and three irrigation frequencies (intervals of F2: 2 days, F4: 4 days, and F8: 8 days) were assessed in 2014, 2015 and 2016 in northwest China. The results showed that the weight of the leaves and leaf stalks was the primary determinant of yield, and that these are the primary N-containing vegetative organs of the plants. At the same irrigation level, the total N content of the plants increased in the order F8 < F2 < F4. The trend in the total N content in the mini Chinese cabbage plants among different treatments was synchronized with the yield. The highest total N content in the plants was observed in the WMF4 treatment during all three years. The three-year averages of mini Chinese cabbage aboveground biomass, yield and water use efficiency (WUE) in the WMF4 treatment were 60%, 64.5% and 119.2% higher respectively than in the CK treatment. The residual NO3-N content in the soil in the WMF4 treatment was only 1.3% higher than that in the CK treatment. The total N uptake in the WMF4 treatment was 79.2% higher than that in the CK treatment, and the N loss in the WMF4 treatment was 46.3% lower than that in the CK treatment. Under these experimental conditions, the WMF4 treatment can be recommended as an appropriate irrigation regime for mini Chinese cabbage under fallow greenhouse management in northwest China.