Identifying spatiotemporal variation of groundwater NO 3 -N and its primary controlling factors are vital for groundwater protection. This study, under the data scarce conditions and based on time series monitoring data in Dagu aquifer, applied methods including hydrochemical ion ratio, multiple linear regression, support vector regression and grey relational analysis and dedicated to revealing primary controlling factors of temporal variation patterns of groundwater NO 3 -N. The results showed that agricultural and manure fertilizer are the main sources of NO 3 -N in north and central area (vegetable farming area), and that domestic sewage discharge and manure fertilizer are the main sources of NO 3 -N in south area (residential and grain planting area). In addition, results identified the dominant influencing factors of variation of NO 3 -N in different regions, with human wastewater discharge, nitrogen load amount and water-table depth being the dominant factors of variations of NO 3 -N in north area, human wastewater discharge being the main factor of variations of NO 3 -N in central area, and irrigation water and human wastewater being the leading factors of variations of NO 3 -N in south area. Moreover, types of controlling factors can influence the seasonal variations of NO 3 -N. NO 3 -N in vegetable farming area that dominantly affected by fertilization generally shows higher concentration and larger variation range of concentration during summer and autumn than that during spring. NO 3 -N which mainly affected by human wastewater discharge and manure inputs shows minimal seasonal variation of mean concentration. NO 3 -N in grain area influenced by irrigation could show more significant variations during spring and autumn than that during summer. The conclusions can enhance understandings of major influencing factors on NO 3 -N variation in local aquifer. Importantly, the dominant roles of water-table depth and irrigation in NO 3 -N variation of N2 site (vegetable planting area) and S5 site (grain planting area), respectively, were highlighted.