Excessive application of nitrogen fertilizer is a widespread problem in vegetable field in Taihu Lake basin, which would not only cause severe non-point source pollution, but also induce soil acidification, and hinder vegetable growth, too. A number of studies have demonstrated that having a strong N adsorption capacity, biochar is able to affect nitrogen recycling in the soil and regulate soil pH in various ecosystems, but little is known about effects on vegetable soils and vegetable production. In this study, impacts of biochar application on vegetable growth, N absorption N utilization, N transformation, soil readily available N and soil pH are explored. A pot experiment was carried out using acidified garden soil collected from Taihu Lake region and biochar prepared out of wheat straw under 450oC. The experiment was designed to have four treatments: biochar and urea (BC+U), only urea (U), only biochar (BC), and no N fertilizer treatment (N0, control) and 6 replicates for each treatment. Five continuous croppings of pakchoi (Brassica chinensis L.) were planted. For the first 3 crops, urea (N 100 kg hm^-2) was applied into related treatments, i.e. Treatments BC+U and U; and for the following two crops, no N was applied soil N as designed as N depletion period. Biomass of and N accumulation, nitrate and amino acid contents in pakchoi and dynamics of soil readily available N was measured during the harvest season. Soil pH was determined at the end of the experiment. Results show that application of biochar significantly promoted vegetable growth, and yield of and N accumulation in the vegetable of the 2rd and 3rd cropping was increased by over 70% and 60%, respectively, in Treatment BC+U as compared with that in Treatment U. In the last two croppings without N fertilization, the yield of and the N accumulation in the vegetable in Treatment BC+U still remained quite high, almost twice as high as that in Treatment U, thanks to the presence of biochar in the soil. N application increased nitrate and amino acid contents in the vegetable, while addition of biochar could effectively decrease nitrate content and significantly increase amino acid content in the vegetable. The apparent N recovery rate of chemical N fertilizer is quite low, ranging from 0.01% to 22%. The application of biochar obviously improved N utilization efficiency. The comprehensive average N utilization rate of the 5 croppings in Treatment BC+U reached 34%, 6.4 times as high as that in Treatment U. Treatment BC+C remarkably lowered the content of soil readily available N left in the soil and the proportion of nitrate-N after the crop was harvested. However, during the N depletion period (the last 2 croppings), Treatment BC+U still maintained a quite high content of readily available N in the soil, which was much higher than that in Treatment U. Continuous application of N fertilizer put soil pH on a declining trend, while addition of biochar dulled the declining trend effectively. Soil pH in Treatment BC+U was 0.5 higher than that in Treatment U. The findings of the experiment indicate that addition of biochar can optimize nitrogen supply of the soil by regulating nitrogen adsorption and release, stimulate N uptake and transformation by the crop, and uphold high yield of the crop. However, as for long-term impacts of biochar application on soil N recycling and crop growth, more in-depth work needs to be done in future.