In order to fully understand the spatio-temporal variability of soil available nutrients in cultivated lands of Weibei Tableland, measured data of soil readily available nutrient contents in cultivated lands of Pucheng, a typical agricultural county of Weibei Tableland, in 1980 and 2011 were gathered and analyzed, using traditional statistics and geo-statistics in combination with GIS technology for spatio-temporal variation of alkalytic nitrogen (AN), available phosphorus (AP) and its affecting factors. Significant differences were found between the two years in content of soil nutrients (p < 0.05 ). In 2011, the average content of AN and AP was 75.11 mg kg^-1 and 19.166 mg kg^-1, respectively, or 84.32% and 179.30% higher than their respective one in 1980, but the mean AN/AP was 5.60 in 2011, 22.33% lower than that in 1980, which indicates that their variation coefficients（CV）of the two periods ranged between 35% ~ 77%, and ranked moderate in intensity. However, CVs of the two soil nutrients both increased, with CV of AP in particular, the CV of AN increased by 1.48% and of AP by15.21%. Obviously in the past 30 years the contents of soil AN and AP in the cultivated lands of Pucheng County increased significantly, with widened span between extremes and intensified variability. The semi-variance function and fractal dimension (FD) analyses of the data show that the contents of AN and AP were higher in 2011 than in 1980 in nugget/sill ratio and in fractal dimension, but narrower in spatial correlation distance. Meanwhile, the spatial autocorrelation analysis reveals that the normalized Z scores of Global Moran’s I of AN and AP were higher than 2.58, which indicates that the two were extremely significant in spatial autocorrelationship (p<0.01) and in spatial clustering．Nevertheless, the Z scores of AN and AP in 2011 were lower than those in 1980. The results of the above-mentioned analyses are quite consistent, indicating that in the past 30 years, the spatial structure features of AN and AP weakened and correlationship lowered. Variation of soil nutrient contents is closely related to their initial values (p<0.01). In soils low in initial value, soil available nutrient contents increased drastically, while in soils high in initial value they increased slowly or even decreased somewhat. Quite obviously, initial values of the soil nutrient contents influence their spatial distribution and evolution patterns. Meanwhile, regions high in AN/AP have turned into regions low in the ratio and vice versa. Though in areas the severe imbalance between AN and AP are corrected to a certain extent, they are still not suitable for cultivation. Besides, impacts of geomorphic type, soil type, land use type, irrigation and fertilization on soil nutrient contents were analyzed．It was found that irrigation and fertilization were the main artificial factors affecting spatio-temporal variation of soil AN and AP．Human activities blurred the influence of natural factors and weakened the correlationship between soil organic matter and other nutrients. Moreover, intensity and emphasis of artificial fertilization enhanced differentiation of landforms and soil types, thus intensifying the correlation between soil nutrient and geomorphic types. Therefore, excessive application of N and P fertilizers and improvement of irrigation conditions contributes most to the increase in soil AN and AP．During the process of cultivation management, effective site specific measures should be taken in formula fertilization and soil quality management.